Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 1:00 PM GMT on May 19, 2009
A complex weather system is bringing showers and thunderstorms over Florida and the Bahamas, in association with a trough of low pressure. Two 1010 mb surface lows have developed--one over the Florida Keys, near 24N 81W, and the other over the south-central Bahamas, near 23N 77W. This second low was designated Invest 90L by the National Hurricane Center yesterday afternoon, and was the first area of interest so designated this year. At that time, they gave it a 30% chance of developing into a tropical cyclone by Wednesday. However, current satellite imagery shows little organization of the cloud pattern and no signs of a surface circulation, and the region is under high shear of 30 knots. 90L is being absorbed into the larger low over Florida, and is no longer a threat to develop, according to a Special Tropical Weather Outlook issued by NHC.
Figure 1. Current radar-estimated precipitation from the Melbourne radar.
The latest 00Z and 06Z runs of the computer models continue to forecast the intensification of an extratropical low near Florida over the next day. The low should bring heavy rain and possible flooding problems to Florida and the Bahamas this week as it moves west or west-northwest into the Gulf of Mexico. Up to eight inches of rain have already fallen over Florida so far (Figure 1), thanks in most part to a cold front that moved over the state during the past two days. Florida could use the rain--most of South Florida is under extreme drought, and Central Florida is under severe drought. The Lake Okeechobee water level is at 10.58 feet, which is about 3 feet below average. During the past week, the lake fell below the level that triggers water conservation measures for the first time since Tropical Storm Fay filled up the lake in August.
I don't expect development of a tropical or subtropical storm over the next two days, due to high wind shear. However, once the system moves into the Gulf of Mexico later this week, the ECMWF and UKMET models are predicting wind shear will drop enough over the northern Gulf of Mexico to allow some development. The GFS and NOGAPS models portray an unfavorable environment with higher shear. I'll give a 20% chance of this system eventually developing into a tropical or subtropical depression in the next seven days. The storm is expected to come ashore over Louisiana on Saturday (NOGAPS and UKMET models), or Sunday over Texas (ECMWF model). The GFS model dissipates the storm over the southern Gulf.
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