Lesser Antilles wave gets better organized; weather radio recall ordered

The tropical wave about 500 miles east of the Lesser Antilles Islands, 94L, has become better organized today, and has the potential to become a tropical depression on Friday. Visible satellite loops show a limited amount of thunderstorm activity, but the circulation has gotten much better defined in the past few hours. Low level cumulus clouds are now starting to spiral into the center, and there is the beginning of a spiral band with heavy rain trying to form on the southeast side of 94L. This process is being slowed by the presence of a large, dusty area of dry air on its northwest side, and thunderstorm activity will be slow to build on this northwest side over the next day or two.

Water vapor satellite loops of the region show that 94L has not significantly moistened its environment. However, now that it is better organized, it should be able to build more thunderstorm activity and moisten its surrounding environment. Wind shear is a favorable 5-10 knots over 94L, and may decrease some by Saturday, allowing further development. It looks like 94L will stay well south of the shearing winds of the upper-level low spinning north of Puerto Rico.

94L has slowed down its forward speed to 10-15 mph, so should be entering the Lesser Antilles Islands on Friday night, bringing gusty winds and heavy rain. None of the reliable computer models forecast that 94L will develop into a tropical depression, but it now appears that it has a legitimate chance of becoming one Friday or Saturday. Due to the dry air, I think it unlikely 94L will be stronger than a 50-mph tropical storm when it passes through the Lesser Antilles Islands. The southern portion of the islands will get the most rain, due to the dry air on the north side of 94L. The Hurricane Hunters are scheduled to investigate on Friday afternoon.


Figure 1. Infrared satellite image showing the various disturbed area of weather in the Atlantic today.

95L and 96L
An area of low pressure ("95L") about 400 miles east of Jacksonville, Florida has an elongated, closed circulation, but very little heavy thunderstorm activity. A separate low ("96L") is about 400 miles east of Cape Hatteras, North Carolina, and has a well defined closed circulation. Heavy thunderstorm activity is limited to a small glob of convection on the southeast side of the circulation, due to strong northwesterly winds aloft creating 10-20 knots of wind shear. QuikSCAT data from 6:08am EDT this morning shows this circulation nicely. Top winds seen by QuikSCAT were 30 knots (35 mph).

The North Carolina disturbance, 96L, is becoming the dominant system, which will make 95L's development slow, since the two systems are so close together. We can pretty much throw out the model predictions for these disturbances, since none of the models properly initialized two low pressure systems in this region. 96L (the North Carolina low) has developed some upper level outflow, and may become a tropical depression tomorrow if the wind shear relaxes a little and allows thunderstorm activity to build on more than just the southeast side of the storm. This system should get caught up in the jet stream and whisked out to sea to the northeast, and at present does not appear to be a threat to any land areas except the Canadian Maritime provinces.

It is possible that outflow from 96L will choke off and kill 95L. If 95L survives, it may have a chance to develop into a tropical depression once 96L clears out. It is less clear what the track of 95L might be, since it is further south where steering currents are weak. I expect 95L may wander erratically for a few days.

There is a Hurricane Hunter mission scheduled for this afternoon to investigate 96L. No missions are scheduled for Friday into this system.

Mexico is watching 97L
An area of low pressure ("97L") is bringing heavy rains to the same part of the Mexican coast inundated by Hurricane Dean. 97L has only about six more hours over water before it moves ashore, and probably does not have enough time to become a tropical depression before doing so.

Coast of Africa
None of the computer models are forecasting the development of a tropical depression during the coming week off the coast of Africa. There is a large surge of moisture with tropical waves embedded in it coming off the coast of Africa this week, so we will need to continue to monitor this area for development.

Weather radio recall
There's a recall of 66,000 Oregon Scientific Weather Radios that was announced today by the U.S. Consumer Product Safety Commission. The radios could fail to receive National Weather Service alert signals in certain areas of the country. In the event of severe weather, this failure could put a consumer's life and property at risk.

Jeff Masters