Category 4 Hurricane Felicia peaks in intensity

Category 4 Hurricane Felicia put on a very impressive burst of intensification yesterday, peaking out with 140 mph winds. Recent infrared satellite loops show that Felicia is maintaining its Category 4 intensity, as the cloud tops surrounding the eye have stayed relatively constant in temperature.


Figure 1. Current satellite image of Hurricane Felicia.

While Felicia is an impressive hurricane now, its days are numbered. Sea surface temperatures (SSTs) under Felicia have already declined 1.5°C from yesterday, and are now 27°C--about 1°C above the 26°C threshold needed to sustain a hurricane. Felicia's west-northwest track will continue to take the storm into a region of cooler waters, which should induce a slow but steady weakening trend, beginning later today. Felicia has a very thick ring of intense thunderstorms surrounding the eye, which is characteristic of a class of hurricanes called "annular" hurricanes. Due to their structure, annular hurricane tend to resist weakening, and Felicia will probably weaken only very slowly at first. By Friday morning, SSTs should fall to 26°C, and decline to 24.5°C by Saturday. Wind shear is expected to remain in the low to moderate range over the next three days, 5 - 15 knots. On Sunday, Felicia will be encountering very strong westerly winds aloft, which should create 30 - 40 knots of wind shear. By Monday night, when most of the models predict Felicia will be nearing the Hawaiian Islands, the high shear may be able to tear the storm apart. Only the GFDL model holds on to Felicia that long, predicting that the storm will be a tropical depression with 35 mph winds when it blows through the Hawaiian Islands. The rest of the models dissipate Felicia by Monday. While the current forecast calls for Felicia to have a minor impact on Hawaii, NHC is taking this storm seriously and has scheduled a flight of the NOAA jet into Felicia on Friday. The jet will drop a series of dropsondes that will be used to gather data that will be fed into tomorrow night's 00Z computer model runs. Regular low-level flights by the Hurricane Hunters are scheduled to begin Saturday afternoon.


Figure 2. The eye of Hurricane Felicia as seen by NASA's MODIS instrument on the Terra spacecraft yesterday. The image was taken at 19 UTC 8/5/09 while Felicia was rapidly intensifying. At the time, Felica was a Category 3 hurricane with 115 mph winds. Felicia peaked in intensity as a Category 4 hurricane with 140 mph winds 9 hours after this photo was taken. Image credit: NASA.

Typhoon Morakot takes aim at Taiwan
Category 1 Typhoon Morakot is headed towards Taiwan, and is expected to make landfall tonight. Satellite loops show that the clouds surrounding the eye are developing very cold tops as they push high into the troposphere, a sign the storm is intensifying. Morakot is expected to intensify into a Category 2 typhoon before making landfall. Storm chaser James Reynolds is intercepting the storm and will be posting live updates on his typhoonfury.com web site and twitter for those who want to follow the storm. The large eye of Morakot is now visible on Taiwan radar.

The Atlantic is quiet
There are no areas of disturbed weather in the Atlantic worth mentioning today, and no computer models forecast tropical storm development over the next seven days.

I'll have an update on Friday.

Jeff Masters