Western Pacific Tropical Analysis: August 9, 2017

After about two and a half weeks, the Noru saga has come to a close at last. In the wake of the prolifically long lived typhoon, not much is left to be discussed as the basin has gone back into its slumber. Upper level subsidence has once again spread over the basin, and the monsoon southwesterlies have retracted back towards Southeast Asia, leaving little available focus for tropical development. The next period of significant tropical development is likely 10-14 days down the road, but as we approach the seasonal activity peak, it will become more and more difficult to keep down at least weak development for an extended period of time.

One coherent disturbance does currently exist over the Tropical Western Pacific. Located well to the east at approximately 14ºN, 174ºE, the disturbance features decent vorticity but lacking convective activity. The area this disturbance is traversing features high 500 mb heights and may be struggling with large scale subsidence. Considering the system’s present consolidation, tropical cyclogenesis cannot be ruled out with the system as it moves northwest and then north into a slight weakness between subtropical ridging, but subsidence and then shear north of 20ºN will likely prevent the disturbance from meeting requirements for a classifiable tropical cyclone. The system will likely be tagged as an invest, however.

Aside from the aforementioned disturbance, it is rather difficult to identify something with tropical cyclone potential over the next week or so. The belt of monsoon southwesterlies associated with last week’s reverse-oriented monsoon trough is now very far north and in the process of cutting off from the parent southwest monsoon. Large scale subsidence has also returned to the Tropical Western Pacific, and 500 mb heights are once again running abnormally high. Overall, conditions do not look favorable for tropical development.

In the medium range, there are some early hints that the monsoon trough may re-establish itself in the basin as subsidence begins to relax a little. Most guidance except American guidance show low level westerlies returning around day 10. I wouldn’t get hung up on American guidance failing to show a similar solution either, since it appears it gets Madden-Julian caught up in the Western Hemisphere, keeping a powerful downward pulse over the Tropical Western Pacific. This is a well-known bias in American guidance. Taking this into account, I’d say chances are rather good that the monsoon trough will make a return to the Philippine Sea, perhaps kicking off the next wave of activity around day 10.

Apologies for the missed post this past weekend as I was feeling rather poor. My next post is slated for this weekend. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: August 2, 2017

Typhoon Noru continues to spin across the Tropical Western Pacific, and the system has been joined by Tropical Storm Nalgae well to the east. Nalgae appears to be no threat to land, but the same cannot be said about Noru. Noru appears to be headed on a collision course for southern Japan and possibly South Korea. Noru has come back down to earth after a period of explosive intensification a few days ago, and some guidance solutions showing similar strengthening are likely overdone, but some strengthening remains possible before final landfall. Aside from the two active storms, no additional tropical activity appears likely over the next several days.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

The ever persistent Typhoon Noru is now approaching two weeks as a named system, an impressive feat. Noru has also generated the most ACE of any Pacific Typhoon since Goni and Atsani of 2015, and it will likely be passing them soon as well. As of 21Z August 2nd, the center of Noru’s now very large eye was located at 27.1ºN, 135.3ºE per JMA. JMA and JTWC’s latest intensities for the system are 85 kt and 95 kt, respectively. These are at or just below (respectively again) each agency’s T5.5 intensity. However, considering the particularly large eye and somewhat lackluster convective appearance, I have a suspicion that these intensities are perhaps a little generous. Regardless, Noru has come back down to earth after explosively intensifying into the first SSHWS category 5 tropical cyclone of 2017 a few days ago.

The defining feature of Typhoon Noru at the moment is the system’s massive eye. The eye both on infrared and microwave imagery measures about a degree and a half, or 90 nautical miles, in diameter. While not the largest tropical cyclone eye observed, it is in the upper percentile. This eye size is even more rare considering it lacks a remnant inner eyewall within it. With such a large core, the upper level outflow needs to be working overtime to properly vent the system. This has not been the case recently. Analyses have shown outflow to the system’s northwest restricted by a passing trough and associated PV streamer. This trough is now departing though, and there are already some early signs that the outflow is beginning to recover.

The aforementioned trough has been a major source of uncertainty in previous forecasts. Noru’s primary steering mechanism for the past several days has been a subtropical ridge to the north. The trough that is in the process of passing by weakened the ridge, and it was initially uncertain if enough of a weakness would be created to allow Noru to escape poleward. However, it now appears that Noru will not be escaping poleward. As the mid-latitude trough departs, the subtropical ridge should restrengthen some to Noru’s north, forcing the system slowly westwards towards the northern portion of Japan’s Ryukyu Islands. This west motion should continue for at least the next two days and at most three. After that, Noru is expected to be picked up by the next trough and recurve to the northeast. The exact recurve point is not yet known, but it does appear like it will occur either in the vicinity of the northern Ryukyus or in the East China Sea just to the west. This means landfall could still come in a variety of locations from anywhere on Kyushu to eastern South Korea, but considering that I expect Noru to continue maintaining an exceptionally large core, the worst of the typhoon could spread unusually far from the centerline. At the moment though, I expect a western Kyushu landfall, near the center of the guidance envelope.

As has been the case with Noru for all its life, the intensity forecast remains far from a walk in the park. Much of guidance has been blowing Noru back up into a very powerful system in the vicinity of the northern Ryukyus. American guidance in particular has been insistent on a system well below 900 mb. However, I continue to remain skeptical of such solutions, perhaps even more now than ever before. As mentioned previously, I expect Noru to maintain an exceptionally large core for the remainder of its life, which will need near perfect outflow for any strengthening to occur. Additionally, upwelling could become an issue for the large, slow moving storm. A strenghening signal does appear to be nearly unanimous in the vicinity of the Ryukyus, and this does seem to be in response to improving upper air conditions. The degree of strengthening is almost certainly overdone though. The HWRF more or less maintains the large cored Noru as a higher end SSHWS category 2 up until landfall, which appears to be a reasonable intensity forecast to me.

The other active system is Tropical Storm Nalgae, with formed from the reverse oriented monsoon trough well to the east of Typhoon Noru. In fact, the location of Nalgae’s birth is almost exactly the same as Noru’s. Nalgae is expected to strenghen some, perhaps nearly or just meeting the criteria for a minimal typhoon before being picked up by the same trough that just missed picking up Noru, sending the system north into the mid-latitude North Pacific.

Development over the rest of the Tropical Western Pacific looks unlikely over the next several days. There is an outside shot that Invest 98W, located to Tropical Storm Nalgae’s east, could organize enough to become classified, but considering the hostile conditions currently assaulting the invest, I do not expect this outcome to transpire.

My next post is slated for either Saturday or Sunday. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: July 30, 2017

Three systems are currently active across the Tropical Western Pacific, although two are currently inland. As it has done for over a week now, the long standing Typhoon Noru continues to spin over the Western Pacific waters, now meandering near the transition waters between the tropics and subtropics. Former Typhoon Nesat is now an entry level tropical storm over eastern China after crossing Taiwan. Tropical Storm Haitang is following closely on the heels of Nesat and now located inland over Taiwan. Some additional brief development may occur in the subtropical waters well east of Noru courtesy of a reverse-oriented monsoon trough, but the bulk of this entry will be dedicated to Typhoon Noru.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

In a season thus far of short-lived tropical cyclones, Typhoon Noru has stood out as a significant aberration. Noru is quickly closing in on ten days as an active tropical storm. With the system now positioned by JMA at 22.9ºN, 141.4ºE as of 12Z July 30, Noru is now south of the Tropic of Cancer for the first time in its life. This southward drop into the transition area between the tropics and subtropics is also accompanied by warmer, more heat laden waters and a more moist surrounding airmass, something Noru has been lacking the past several days. Coupled with light upper level winds, it should be no surprise to see Noru strengthening.

With 12Z intensity estimates of 80 kt and 95 kt from JMA and JTWC, respectively, the system has rapidly intensified from just under typhoon strength to 5 kt below each agency’s T5.5 intensity. On first glance, this sudden burst of intensification appears somewhat surprising, but perhaps it shouldn’t be. 37 GHz microwave imagery from about 48 hours previous to this post revealed good structure featuring a cyan eyewall ring, despite Noru struggling with the dry surrounding airmass at the time. In the presence of favorable conditions, a cyan ring on 37 GHz microwave imagery is usually an indication that rapid intensification is about to commence. Subsequent Coriolis and AMSR2 passes over the next 24 hours showed the continued presence of this cyan ring. Over the past 12-18 hours, Noru has moved into a more favorable environment, as mentioned in the paragraph above, and it appears that Noru’s surprisingly good structure has allowed for rapid intensification. I can’t quite place why Noru’s structure was able to consolidate while struggling with dry air and weakening below typhoon intensity, but if I were to speculate, the light to non-existant wind shear present over the system allowed the structure to remain undisturbed, despite the repeated and almost constant dry air intrusions. With newfound favorable conditions, Noru has intensified to its strongest yet. Constrains obviously come into play, but raw and instantaneous Data Ts are currently up near 7.0.

Noru’s drop to the south is in direct response to a subtropical ridge strengthening just to the system’s north, shoving the system south. This now-established ridge will be the primary steering mechanism for Noru over the next couple of days, although Noru will not be moving much. A slow westward motion is the primary expected motion for this period. After this, a passing mid-latitude trough will begin eroding the steering subtropical ridge, and Noru’s steering will again break down. A slow drift with a poleward component appears to be the preferred solution appears to be a common theme amongst guidance, but the degree of lateral movement at the same time is uncertain. Such motion could eventually make a big difference for Noru’s ultimate future, and a further westward positioning could eventually result in a trough capture that sends Noru into Japan. European guidance has consistently favored the western drift over an eastern one, and most of the strongest members amongst ensemble suites lie near the western side of their spreads. Considering Noru’s ongoing rapid intensification, I am biasing my track philosophy towards the left side of the guidance envelope, although the weak steering and large spread inherently leads to a low confidence forecast. My track would be a little left of, but very near both JMA’s and JTWC’s track forecasts.

Intensity forecasting is again tricky. Noru is and will be over waters warm enough to support a rather intense storm, but with the system’s slow movement, upwelling could eventually become an issue. Peak intensity may actually come in the near term with the current bout of rapid intensification, which may bolster Noru near or even surpassing the threshold for super typhoon intensity. Inner core dynamics may come into play following this bout of rapid intensification however, and it wouldn’t surprise me to see eyewall replacement begin in about 24 hours or so. Upwelling may come into the picture at this point, but I do expect other factors to remain favorable for Noru. At this point I expect Noru to be above SSHWS category three for the few days.

Tropical Storm Haitang has recently made landfall over Taiwan. The system was not particularly strong at landfall, but the system does feature some very deep convection. The one-two punch of Nesat and Haitang for Taiwan and eastern China could result in numerous flooding issues.

Extending to the south and east of Typhoon Noru is a reverse-oriented monsoon trough. Guidance has backed off considerably regarding the quantity of systems consolidating and emerging from the feature, but it still appears likely that at least one system will manage to develop well to the east of Noru. Considering the elevated latitude that the reverse-oriented monsoon trough is currently found at, any emerging system will likely remain on the weaker side before shooting off into the mid-latitudes.

My next scheduled post is slated for Wednesday. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: July 26, 2017

Since my last post a week ago, an amazing five tropical storms have developed across the Tropical Western Pacific. Typhoon Noru and Tropical Storm Kulap developed over the basin’s subtropics, very small Tropical Storms Roke and Sonca developed on either side of Luzon, and the recently named Tropical Storm Nesat has emerged from the monsoon trough in the western Philippine Sea. Noru, Sonca, and Nesat are still active currently, although Tropical Depression Sonca hardly counts since it is now well inland over Southeast Asia. It is possible that additional storms may develop in the coming days, but thanks in part to weak steering currents, the establishment of a reverse-oriented monsoon trough, and possible storm interactions, the predictability in the current forecast period is remarkably low.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

Having existed for over five days now, Typhoon Noru is the longest-standing storm in the basin and, if some of the guidance solutions are to be believed, could possibly still be hanging around ten days from now. As of 1500Z July 26, a satellite bulletin from JTWC placed Noru at 30.18ºN, 154.59ºE. JMA’s and JTWC’s latest intensity estimates for Noru are 70 kt and 80 kt, respectively, making it the first typhoon of the 2017 Pacific Typhoon Season. Noru has spent its life thus far looping around the subtropical waters of the Western Pacific.

Noru’s steering has been dominated by two factors the past several days, a blocking mid-latitude ridge and Tropical Storm Kulap. The former has prevented Noru from escaping north into the mid-latitudes, while the latter resulted in Fujiwhara interaction between the two systems. The interaction helped to keep Noru further east in some more favorable conditions while Kulap was flung westward to Noru’s north, where it met its demise in more hostile conditions. With Kulap now gone, Noru is again able to move west and then west-southwest as the primary steering mechanism transitions from a mid-latitude blocking ridge to a subtropical ridge anchored over the northern East China Sea between China, South Korea, and Japan. Members of guidance are actually in good agreement in the near term with this scenario. Conditions along the way will likely be similar to what the system is experiencing now: enough dry air to keep a lid on intensification, but favorable enough otherwise. I would not be surprised to see Noru remain within 10 kt of its current intensity as it carries out its west-southwestward dip over the next four days.

From then on, the forecast gets more dicey. After completing the west-southwestward dip, Noru will be over warmer waters than those found near 30ºN where the system currently is, but also in close proximity to Nesat and a strengthen monsoon trough extending eastwards. In other words, steering becomes very complex, and forecasting beyond four days out becomes a nightmare. The current trend in guidance has Noru heading back east beginning around day five around 25ºN while possibly interacting with new monsoon trough development, but previous solutions have shown everything from escaping north to interacting with Nesat until one or the other’s demise. Some guidance (particularly American guidance) continues to blow Noru up into an exceptionally powerful storm, but I remain skeptical of such solutions. This skepticism has paid off thus far, as Noru has yet to become a major typhoon. Forecasting intensity with so much uncertainty with everything else remains a fool’s errand anyhow, but if forced to put out an intensity forecast for the taus beyond hour 96, it would probably remain very near the current analyzed intensity.

The following tweet from Philippe Papin explains not only the uncertainty with Noru, but in the entire basin far better than I can.

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I want to briefly touch on Tropical Depression Sonca. Sonca made landfall along the Vietnam coast over 24 hours ago from the time of this entry, but the system has held together amazingly well as it treks inland across Southeast Asia. As mentioned, JMA is still classifying Sonca as a tropical depression despite having crossed about half way to the Bay of Bengal. As expected from a system well inland, Sonca’s biggest threat will come in the form of heavy rain.

Tropical Storm Nesat is the newest of the currently classified systems in the Tropical Western Pacific. As of 1800Z July 26, a JTWC satellite bulliten placed Nesat at 17.40ºN, 127.64ºE. Nesat is the system I first mentioned in my July 16th entry that would consolidate along the monsoon trough in late July. Nesat’s development has been just about the only thing that has been predictable in the Tropical Western Pacific recently, and keeping with the recent theme, that predictability only goes down from here.

As seen in the loop above, Tropical Storm Nesat is characterized by strong, cold central core convection. However, it appears that the system may be taking on the Central Cold Cover pattern, or CCC pattern. Such patterns are usually a result of some mid-level shear undercutting the anvil, and bands 9 and 10 from Himawari-8 do indicate that light northerly shear of this variety is occurring. A recent GPM pass also indicates that most of Nesat’s convective structure is confined to the south of the center. Considering Nesat’s present state, development in the immediate short term if any should be slow to occur.

Nesat is currently moving with a slow north-northwestern motion. This general motion to the northwest or north-northwest should continue for the next couple of days. At the time, it appears that will remain far enough away from Noru to avoid any direct interaction with the typhoon, but such a scenario cannot be completely ruled out at this time, especially if Nesat tracks a little slower than currently expected. As it stands right now, Nesat is expected to be near Taiwan by tau 72. Northerly and then easterly shear may be something that Nesat has to contend with its entire life, but it is possible that the system could intensify into a typhoon before landfall.

92W is one of the two invests currenly declared across the Tropical Western Pacific. Located in the South China Sea, 92W is developing along the same monsoon trough that Tropical Storm Nesat emerged from. It is possible that development could occur with this invest, but easterly shear, partially from the larger and stronger Nesat, would likely keep any development weak before moving inland into southern China.

Invest 93W is the other active invest. The system is located well east in the basin’s subtropics, near where Kulap originated from. At the moment, I do not expect development due to the magnitude of vertical wind shear, but this is an area worth keeping an eye on, especially once Noru moves WSW and helps draw out monsoon southwesterlies across the basin.

As mentioned early on in this post, more development is possible over the next several days as the monsoon trough begins to extend well east across the entirety of the basin. The monsoon trough is expected to take on a reverse-orientation (more north the further east along the monsoon trough, opposite of a typical setup), extending the eastern end well above 20*N. Such a scenario offer up not only an opportunity for multiple new storms, but also interactions between these yet to develop system. Guidance almost always struggles with such a scenario, but most members agree on the general idea. The specifics remain to be seen though, and I’m not even going to pretend to know how it will all play out. Partially for entertainment purposes, the 12Z July 26 GFS run is provided below.

Thank you all for being patient with me getting this new post up as I have been dealing with moving into a new place. The next update should be up this weekend. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: July 19, 2017 – Subtropic Shenanigans

After an exceptionally quiet start to the 2017 Pacific Typhoon Season, the Tropical Western Pacific is about to enter a more active period, and some of this activity appears like it will becoming from some unlikely sources. Three invests are currently declared across the basin, and all have at least some shot at earning a name. From west to east, invests 95W and 97W are currently located over the eastern waters of the Subtropical Western Pacific, and hail from non-tropical origins. Invest 95W, which is also a JMA tropical depression, probably has the most immediate chance at development in the basin, but the future of 97W looks particularly interesting. Invest 96W resides in the South China Sea and has a chance to follow in Talas’s footsteps. The remnants of a convective complex off the southeastern Kyushu coast may also become tagged as an invest at some point. The monsoon trough also returns to the Philippine Sea this week, and the potential for development here beyond the five day period appears higher than average.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

Of all the development prospects, Tropical Depression/Invest 95W is presently the furthest along. Per JMA as of 18Z July 19, the system was positioned at 26.5ºN, 161.2ºE and moving with only a slow westward drift. JMA has begun to issue advisories on Tropical Depression 95W, meaning that they are expecting to upgrade it to a tropical storm within 24 hours. Should their current forecast verify, it would be named “Noru.”

95W is one of two invests currently designated that have non-tropical origins (the other is 97W a little to the east). Unlike with 97W though, the low level vorticity isn’t now just working its way down to the surface and has been around for a few days. The most recent ASCAT pass of 95W revealed a fairly organized but not quite closed circulation with winds of 25-30 kt just east of the center. Considering the improved convective evolution and development of upper level outflow since the time of that pass, it’s not hard to imagine that 95W could end up being named as the JMA is currently forecasting. In fact, I would be surprised if 95W is not named at this point. Regardless, 95W will be in no hurry moving to the WNW and then NW as it rounds the southwestern edge of a blocking mid-latitude ridge.

Intensity guidance is not particularly aggressive with 95W, and the only member that brings it above the 64 kt typhoon threshold is the HWRF. Considering the abnormally warm waters that currently reside in the Subtropical Western Pacific, moist surrounding airmass, and sheltered location from stronger upper level winds below the blocking ridge, such a forecast doesn’t seem outlandish. However, I’d be more inclined to think a 50-60 kt peak intensity is more likely. Favorable conditions will only last about 96 hours at most before 95W arrives in the hostile exit region of a splitting jet rounding the top of the subtropical ridge centered over China.

Back in the South China Sea, a disturbance located near the eastern end of a weak monsoon trough has been designated as Invest 96W. As of 18Z July 19, the ATCF position for 96W was at 13.7ºN, 116.4ºE, or just west of the Philippines. 96W has been characterized by intermittent and disorganized bursting convection and does not appear to be particularly well marked at the time. 96W is currently experiencing a decently favorable setup reminiscent of the recent Tropical Storm Talas. In fact, 96W is expected to follow a very similar path to Talas. However, 96W’s initial organization is not on par with Talas initially. This difference in organization may prevent 96W from becoming a classifiable tropical storm. With about 72 hours before the system is expected to move inland near the China/Vietnam border, it wouldn’t catch me off-guard to see 96W develop. However, the poorer initial organization coupled with a slightly weaker belt of monsoon southwesterlies make me believe that no development is the most likely outcome.

The last and probably most interesting of the three currently designated invests is 97W. Like 95W, 97W currently resides in the waters of the Subtropical Western Pacific. As of 18Z July 19, the ATCF position for 97W was at 24.1ºN, 178.6ºE. This places 97W to the east of 95W and very near the boundary of the basin with the Central Pacific. 97W is an upper level low that has begun to work its way down to the surface.

Invest 97W has become somewhat of the guidance’s darling as it meanders northwest and then west-northwest across the Subtropical Western Pacific. After fully working its way down to the surface and becoming warm core, the majority of the last few guidance suites have blown up 97W into an intense system over the Subtropical Western Pacific. This is a fairly unusual solution; intense systems are fairly rare in the Pacific subtropics. Most of the intensification appears to occur after the system has moved to the northwest some, into approximately the area vacated by 95W. As previously mentioned, it is an area of sufficiently warm sea surface temperatures, abundant moisture, and low shear, so strengthening shouldn’t be totally unexpected. However, climatology does not favor some of the sub-950 mb solutions seen in recent guidance.

While modeled conditions currently look favorable for 97W over the next week, it won’t take much to introduce some hostilities. 97W is currently dancing around near the subtropical jet stream. The subtropical jet stream is currently expected to weaken and move east-southeastwards away from 97W. However, should it exert its influence on 97W longer than expected, the more intense solutions would fail to come to fruition. Alternatively, the splitting jet expected to impact 95W could extend eastwards and bring upper shear to 97W or the blocking mid-latitude ridge could introduce dry air subsidence trough subsidence that 97W could then entrain. The point is it takes absolutely perfect conditions to be maintained for an appreciable time period to get a strong system in the subtropics, and I’m not entirely sold that is currently the case. At the moment, I am expecting 97W to achieve a maximum intensity of 75-85 kt in about 5 days. However, at this point, this is an extremely low confidence forecast. The one thing that is almost for certain is that 97W should make for an entertaining system to track after an exceptionally quiet start to the 2017 Pacific Typhoon Season.

One more system that is not currently designated but deserves a mention currently lies off the southeast coast of the Japanese island of Kyushu. The system originates from a Mesoscale Convective Complex that moved off the coast about 24 hours ago and appears to be gaining some organization. However, the window for this system to develop is rather small. Strong upper level northeasterly winds are expected to begin raking over the system in about 36 hours, undoing any organization that occurs up to that point. Brief development isn’t an impossibility, but it is also not expected at this time. It wouldn’t surprise me to see this system tagged as Invest 98W though.

In addition to all the current systems in various states of development, the monsoon trough is expected to extend back to the east and into the Philippine Sea within the next five days. It is around that time that guidance is beginning to pick up on an emerging system in the Philippine Sea. It’s still too early to forecast an intensity for a system that has yet to even form an initial disturbance, but I do believe that this potential system’s ceiling is the highest yet observed the season. Whether that potential is realized is yet to be seen, but confidence in development is considerably higher than average. This possible system is most likely to track northwest or north-northwest into a break in subtropical ridging, in the general direction of Taiwan and the southern Ryukyus.

My next entry will likely arrive this weekend, but with packing and moving in my near future, it is not a 100% certainty. Until the next entry arrives, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: July 16, 2017

After a surge in the Southwest Monsoon, Severe Tropical Storm Talas has managed to develop in the South China Sea and headlines the Tropical Western Pacific. After skirting Hainan, the system is headed for a north-central Vietnam landfall, and Talas brings the threat for heavy rainfall along its track as it moves inland. Talas is the only system to monitor in the near term, but there are some signs in the medium range that the Southwest Monsoon may extend back across The Philippines, reestablishing the monsoon trough in the Philippine Sea in late July.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

As mentioned, Severe Tropical Storm Talas is currently the center of attention in the basin. As of 12Z, Talas was positioned at 18.5*N, 107.2*E. This is along the southern edge of the Gulf of Tonkin, and closing in on the north-central Vietnam shoreline. 50 kt is the consensus intensity estimate from both JMA and JTWC at the time.

Talas has strengthened more than I had expected thus far. I was skeptical it would gain enough organization to become classified in the days leading up to its development, but persistent convective activity near the vorticity maximum allowed the system to properly consolidate and become a named system while in the open water of the South China Sea. Since that time, Talas has managed to steadily strengthen up to the time of this post. As of 06Z July 16, Talas even managed to meet JMA’s 50 kt severe tropical storm threshold, the intensity it still carries as of the most recent 12Z analysis. However, time has just about run out for Talas, and the system will be making landfall on the Vietnam coastline in a matter of hours. Heavy rainfall is the greatest threat Talas carries with it as it moves inland across Southeast Asia.

Elsewhere across the Tropical Western Pacific, conditions remain generally hostile for tropical cyclone development. The tropical upper tropospheric trough (TUTT) remains oriented east/west along 20*N across much of the basin, and a breakoff TUTT low is currently traversing westwards across the Philippine Sea. Mid-level heights also remain higher than usual, indicating subsidence from the upper levels remains an issue. However, arguably the biggest issue that currently is plaguing the basin is the lack of low level equatorial westerlies extending east across the basin. These westerlies, associated with the Southwest Monsoon, are essential for establishing the monsoon trough, from which the vast majority of basin activity originates. Without these monsoon westerlies/southwesterlies, and by extension the monsoon trough, it becomes much more difficult to get tropical cyclogenesis, even with otherwise favorable conditions.

In the near term, not much is expected to change across the Tropical Western Pacific. However, guidance appears to be trying to bring the monsoon trough back in the medium range. Beginning in about seven days, ensemble means extend the monsoon southweserlies back across the Philippines and into the Philippine Sea. It’s too early to be confident in any type of tropical cyclogenesis around that period, but coupled with falling mid-level heights, conditions appear to be trending towards more favorable conditions towards the end of July.

My next entry will likely arrive by Wednesday. Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.

Western Pacific Tropical Analysis: July 13, 2017

The Tropical Western Pacific remains rather quiet at the moment, but at least two area will have a non-zero chance for tropical development in the next few days. The first area is currently located in the subtropical waters south of Japan has been tagged as Invest 93W. The window for 93W is brief though, and I do not expect it to develop. The second area is only just becoming discernible in the South China Sea as a modest surge in the Southwest Monsoon begins to transpire. While I do believe that development chances are higher with this emerging disturbance than they are with 93W, development prospects are still not especially good. Should it develop, the system’s ceiling will remain very low. No other areas are expected to emerge with development prospects over the next seven days.

***NOTE: While I would consider myself well-learned in meteorology, I am still a student with more to learn before becoming a degreed meteorologist. This forecast is not from an official source and should not be treated as such. For official information, please refer to your local weather agency.***

As mentioned my previous entry, a piece of energy became orphaned from its parent system from the mid-latitudes. This system has lingered in the subtropical waters south of Japan near Chichijima for the past couple of days. In that time it has gained enough organization to become tagged as Invest 93W. As of 18Z July 12, 93W was positioned at 25.1*N, 140.8*E. An RGB composite visible loop of 93W is provided below

As it stands right now, 93W is probably near the zenith of its organization. From this point onwards, it will likely begin a losing battle with westerly shear and dry air (both seen in the July 13 00Z Chichijima sounding). An upper level low is located to the system’s north is the primary reason for these increasingly hostile shear, and the dry air is in constant supply due to upper level convergence/subsidence on the system’s northwest flank. These two factors will bring 93W to its demise over the next 2 or so days as it continues to meander the subtropical waters in the vicinity of Chichijima.

Further to the southwest in the Tropical Western Pacific, a modest surge in the Southwest Monsoon is beginning to ramp up across the South China Sea. This surge is amplifying convergence near the tip of the low level jet, leading to increased convective activity. Over the next few days, surface pressure falls from this thunderstorm activity should help to spawn a broad and weak circulation. The 12Z EMCWF’s depiction of this evolution is provided below.

The main question with this potential system is will it have enough time to tighten its broad monsoon circulation enough to be classified before moving inland over southeastern Asia in about four days. At the moment, I am leaning a little more towards it staying too broad, giving it about a 40% chance at classification. Even if it does earn classification, any system that develops will remain weak due to the time constrains mentioned above.

Aside from these two prospects, the Tropical Western Pacific will remain uncharacteristically hostile for at least the next week. At the low levels, there is very little hint of any monsoon southwesterlies anywhere east of the Philippines. Without these southwesterlies needed to maintain the monsoon trough, any disturbances along the Intertropical Convergence Zone have been weak and unable to develop. Aloft, 500 mb heights remain higher than normal, indicating continued upper level subsidence. An anticyclonic wave break in the mid-latitude Western Pacific has also helped to reinforce the Tropical Upper Tropospheric Trough, which is currently covering an abnormally large area across the heart of the basin. Both the 500 mb normalized height anomalies and 355 K Potential Vorticity from the July 12 18Z GFS is displayed below.

If no tropical development occurs by this weekend, 2017 year to date Accumulated Cyclone Energy (ACE) will fall below that of 2010, making 2017 one of the three least active seasons up to that point since 1970.

My next entry will be posted this weekend (Probably Sunday). Until the next entry is posted, analyses and updates in forecast philosophy will arrive in the comments section.