Weatherdem's Weblog

Bridging climate science, citizens, and policy

Atlantic Tropical Weather Update 9/1/09

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[Update 3:00P MDT]: Tropical Storm Erika has formed.

The NHC had hurricane hunter aircraft investigate the tropical disturbance known as Invest-94 this afternoon.  They have reported that a broad-scale, but closed circulation was found.  Directly sampling the environment, they found sustained wind speeds of 50mph near the “center”.  This means the storm is a Tropical Storm.  The difficulty of ascertaining the storms’ characteristics from satellite data isn’t new – remote sensing will always have its disadvantages to go along with its advantages.

Tropical Storm Erika’s vitals are as follows: center located near 17.2N, 57.3W; moving WNW @ 9mph; maximum sustained winds of 50mph; minimum central pressure of 1007mb.

There isn’t any change in the official track forecast – it takes the storm to the north of the northeast Caribbean Islands the next few days.

Tropical Storm Erika should continue to be a Tropical Storm over the next few days as it fights some wind shear on the western side of the storm.


Invest-94 stubbornly refuses to get enough organization and structure to be classified as a Tropical Depression or Storm.  Meanwhile, it draws closer to land forms in the western Atlantic Ocean.  Here is Invest-94’s vitals as of this morning:

“Center” located near 16.8N, 57.2W; moving WNW @ 9mph.

The tropical disturbance has gone through fits and starts of rather impressive thunderstorm development, but has suffered from a lack of a well-defined closed-off low pressure center.  Some mid-level shear influences are currently thought to be the cause of the lack of organization.

The official track forecast, such as it is, takes Invest-94 to the north of the Caribbean Islands, such as the northern Windward Islands, Puerto Rico and Hispanola.  A wide spread in final position still exists for Days 4 and 5, when the system could be anywhere from north of the Bahamas on it way toward the Carolinas to just north of Hispanola, steering towards the southeastern Bahama Islands.

The official intensity forecast is as muddled as the track forecast.  Models continue to call for intensification, which hasn’t happened the past three or four days when the models were very excited about developing the storm.  Hurricane hunter aircraft are on the way today, and should shed more light on local storm conditions and help pin down exactly what’s spinning over the ocean.

The tropical wave that exited Africa yesterday is centered just east of the Cape Verde Islands.  The NHC has labeled the area of disturbed weather as an area of interest, giving it <30% chance of tropical development in the next 48 hours.

So, a temporary lull in tropical activity in the Atlantic exists while Category 4 Hurricane Jimena bears down on the Mexican Baja peninsula.  Hopefully damage and lives lost are kept to a minimum there.


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