Tropical Storm Saola Forms, Targets Taiwan
After a few days of quiet in the wake of Typhoon Guchol, the tropics have come alive again, and once again the action is in the West Pacific. The Joint Typhoon Warning Center is issuing advisories on newly named Tropical Storm Saola. As of the latest JTWC advisory, Saola is located approximately 265 nautical miles east of Manila, Philippines. It is moving WNW at about 14mph. Saola currently has maximum 1 minute sustained winds of 35kts, or roughly 40mph, making it a minimal tropical storm. The disturbance that developed into Saola has already produced flooding rains in the Philippines.
Forecast for Saola
Saola is in a very moist environment and over very warm waters, both important factors in determining how much, if any, a storm can strengthen. The other main factor is wind shear. Saola is currently in an environment of fairly light shear. Its track, however, will take it into an environment of more moderate shear, so the main question for intensity will be how it handles this shear. The JTWC forecasts steady strengthening to a peak of 75kts before landfall on Taiwan. One thing that could help Saola is its very large size. This will likely help prevent shear from seriously disrupting the system. I generally agree with the JTWC intensity forecast. If anything I would forecast a slightly higher peak intensity, possibly 80-85kts, due to the possibility that it takes advantage of its current favorable environment to strengthen more in the short term than forecast. However, as we have seen with large storms in the past, they sometimes struggle to bring their winds up due to their large circulations, so a lower than forecasted peak is also possible, though less likely.
Figure 1: Tropical Storm Saola.
Figure 2: West Pacific shear and shear tendency.
The track forecast is very difficult as models are in poor agreement. A ridge is steering the system in a generally WNW to NW direction. Some models, most notably the ECMWF, favor a stronger ridge that would drive Saola further west, while others, including the GFS, show an abrupt right turn in the near future. The JTWC thinks these models may be showing an interaction with a potential developing storm (Invest 95W) to its northeast. This solution seems unlikely however, so the JTWC has opted for a steady NW track that brings Saola into Taiwan in 4-5 days.
Figure 3: Official JTWC forecast track, showing a large cone of uncertainty.
If the intensity forecast holds then Saola would come into Taiwan as a Category 1 typhoon. Heavy rains and especially dangerous mudslides on the mountainous island will be the main threats if it comes in that direction, with gusty winds and storm surge lesser threats. After landfall in Taiwan Saola is likely to turn more WNW instead of NW, bringing it into China about 2 days after landfall in Taiwan. It would likely weaken some over Taiwan and possibly restrengthen slightly after reemerging over water before landfall. This is all subject to change, however, as the JTWC acknowledges that this is a low confidence forecast.
Another disturbance in the West Pacific, Invest 95E, is being watched for development. It is struggling with shear as its center is fully exposed. However, the JTWC still thinks this system will develop soon as they have issued a Tropical Cyclone Formation Alert for it, meaning it is likely to develop in the next 24 hours. I will write an update should this system form. The Atlantic and East Pacific are both quiet with no areas currently being watched for development. Waves continue to roll off the African coast, and some models, including the GFS and NOGAPS, have shown some weak development. Any significant development is unlikely, however, due to unfavorable conditions in the Tropical Atlantic and Caribbean. Multiple models have shown the potential for East Pacific development in the next 10 days, particularly the ECMWF, so I think it is likely we'll see Gilma by August 5th.
Figure 4: Invest 95W
Thank you for reading, and enjoy your weekend!