Tropical Storm Watches for Guillermo; 95L Clips Coast; Soudelor Still a Super Typhoon

Tropical storm watches were hoisted Tuesday morning for the islands of Hawaii, Maui, Molokai, Lanai and Kahoolawe as Tropical Storm Guillermo headed toward the island chain. At 5:00 pm EDT Tuesday, Guillermo was located about 400 miles east of Hilo, packing sustained winds of 70 mph. Wind shear continues taking a toll on Guillermo, with most of the storm’s convection shunted to its northeast side. Drier air and increasing wind shear along Guillermo’s path should prompt a weakening trend later tonight or tomorrow, despite sea-surface temperatures that remain above 27°C (1°C to 2°C above average) along Guillermo’s path. Even the southernmost dynamical model (ECMWF) keeps Guillermo’s west-northwest track far enough north of the islands to avoid tropical storm impacts. NOAA’s probabilistic wind guidance gives less than a 10% chance of tropical storm force winds over Hawaii in the next 120 hours.


Figure 1. A composite (RGB) satellite image of the increasingly sheared Tropical Storm Guillermo, collected by the GOES West satellite at 2200 GMT Tuesday (6:00 pm EDT). Image credit: NOAA/NESDIS.


Figure 2. GOES infrared satellite image of Invest 95L, from 2145 GMT Tuesday (5:45 pm EDT), shows convection mainly offshore of North Carolina. Image credit: NOAA/NESDIS.

Invest 95L clips the Carolina coast
After it triggered widespread flash flooding and river flooding over central Florida, especially in the Tampa Bay area, Invest 95L has been kinder to the southeastern states. At 4:35 pm EDT Tuesday, the National Hurricane Center placed the center of 95L near Wilmington, NC, moving northeast very near the coastline. A large but disorganized shield of showers and thunderstorms has remained mainly southeast of 95L’s center, sparing the Carolinas from much impact side from pockets of heavy rain near the Outer Banks. Reconnaissance flights found offshore flight-level winds of 60 mph at 4:35 pm EDT Tuesday in gales southeast of the center, but winds have been quite light along the coast near 95L, generally less than 20 mph both inland and at near-shore buoys. Phase-space diagrams from Florida State University show that 95L is already exhibiting characteristics of a cold-core system, and the asymmetry of 95L should grow as it shoots northeast and becomes entangled in a midlatitude frontal system. Still, NHC gives 95L a 30% chance of organization over the next several days, and several dynamical models suggest the system could intensify just enough to potentially earn it a name over the next 24-36 hours.


Figure 3. Visible image of Super Typhoon Soudelor, collected by the MTSAT satellite at 2201 GMT Tuesday (6:01 pm EDT). Image credit: NOAA/NESDIS.

A slightly weaker Soudelor threatens Taiwan
Having completed an eyewall regeneration cycle, Super Typhoon Soudelor was sporting a less impressive convective shield and slightly weaker sustained winds on Tuesday, but it remained a formidable storm. Peak sustained winds were estimated by the Joint Typhoon Warning Center (JTWC) at 130 knots (around 150 mph) at 1800 GMT (2:00 pm EDT) Tuesday. Soudelor remains on a classic west-northwest path around the south side of an upper-level ridge, and models are still in close agreement on a landfall in Taiwan on Friday night or Saturday morning local time. The JTWC is calling for gradual weakening over the next couple of days, mainly due to subsidence related to a nearby tropospheric upper-level trough (TUTT). Apart from the TUTT, conditions are highly supportive of some eventual restrengthening. Category 4 strength is possible at landfall, according to the JTWC forecast from 2100 GMT Tuesday (5:00 pm EDT). Soudelor could end up even stronger than predicted if another rapid intensification cycle were to take place (such cycles are difficult to predict in advance). Soudelor will likely go on to strike mainland China as a strong tropical storm or Category 1 typhoon.


Figure 4. Flooding caused by heavy rain brought by Typhoon Morakot across Pingtung county, southern Taiwan, on August 8, 2009. Morakot, which means 'emerald' in Thai, dumped more than 1,255 millimetres (49 inches) of rain on southern Pingtung county. Image credit: AFP/AFP/Getty Images.

Taiwan is familiar with the strong winds and torrential rain brought by major typhoons. From 1897 to 2003, the island recorded 383 typhoon landfalls, an average of about 3.5 per year. Despite this experience, the nation remains vulnerable to flooding and landslides/mudslides, given its dense infrastructure and population and the unavoidable nature of its highly mountainous terrain. The most disastrous storm in recent years to strike Taiwan was 2009’s Typhoon Morakot, which caused more than 450 deaths and some $3.3 billion US in damage. Morakot was only a Category 1 storm, with peak 1-minute sustained winds of 90 mph, but it moved in a leisurely cyclonic loop across northern Taiwan, prolonging the widespread intense rainfall. A 2011study in the Journal of Geophysical Research found that Morakot’s slow motion and interaction with a monsoon-related belt of southwesterly winds played major roles in the disaster. Morakot brought Taiwan its all-time rainfall records for a 24-hour period (1403 mm or 55.2” at Weiliaoshan) and for a 48-hour period (2327 mm or 91.6” at Alishan). Soudelor is a powerful typhoon, but its expected motion at a steady clip across Taiwan should help reduce the risk of such exorbitant rainfall totals.

Our next blog update will be courtesy of wunderblogger Steve Gregory, who is planning a guest post early Wednesday afternoon (around 2PM CDT). You can follow Steve’s regular posts at his WU site.

Bob Henson