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.