Tropical Storm Erika was downgraded to a Tropical Depression on Thursday and its prospects for a much longer life are not real good. The track of the storm ended up being much different from the official forecast which was generally right down the middle of the biggest outlying models. The track had been taking it up just north of the Bahamas. Well, it has generally drifted west more in line with the model tracks that were farther south, or showed a more westerly track and so the NHC altered the track more westerly, until the final update. Trouble with the more westerly track is that it takes the storm over land areas, much of it mountainous areas such as the Dominican Republic and Cuba. In this case, there is also the bugaboo that has always been in the forecasters’ minds and that is a strong shear developing. Keep in mind too that earlier spaghetti models also had a huge spread with some models keeping it at tropical storm strength or below and all the way up to Cat 3 status, and at one time there was more than one that suggested the more robust status. This was a little weird because the models that had the stronger status seemed to be totally discounting the data that advertised increased shear.
However, note that even for 00Z Friday, the BAM model still wants to take it westward and that was the model that the NHC had been influenced by with its guidance. The BAM track is the only one that has the more southern route and there are still two models that want to make Erika a category two hurricane. The new NHC forecast track goes back to the more northwesterly direction toward the bahamas, but still over some pretty tough terrain. Very odd to have such a spread in the consistency after a storm has been around for so long but probably reflects just a crappy structure for a storm.
Anyway, the storm has drifted west and is expected to continue to do so with perhaps some shift more WNW. But, not only will it be running into mountains, it will also encounter shear and suffer from dry air intrusion. In the end, there is just too much working against this storm to make one expect anything more than a rainmaker.
TROPICAL DEPRESSION ERIKA DISCUSSION NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
1100 PM AST THU SEP 03 2009
ERIKA CONSISTS OF A TIGHT SWIRL OF LOW CLOUDS ACCOMPANIED BY A SMALL
AREA OF DEEP CONVECTION TO THE SOUTHEAST. THIS FEATURE IS CURRENTLY
OBSERVED ON SAN JUAN PUERTO RICO RADAR. IN ADDITION…RAOB FROM THE
LESSER ANTILLES SHOW A STRONG MID-LEVEL CIRCULATION ASSOCIATED WITH
ERIKA THAT HAS BEEN LEFT BEHIND OVER THE NORTHERN LEEWARD ISLANDS.
BY TRACING THE CIRRUS CLOUDS ON SATELLITE…ONE CAN CLEARLY SEE
THAT THE SYSTEM IS APPROACHING AN AREA OF EVEN STRONGER
SOUTHWESTERLY UPPER-LEVEL WINDS. THESE WINDS WILL KEEP THE SYSTEM
DECOUPLED AND WILL LIKELY REMOVE ALL THE ADDITIONAL CONVECTION THAT
COULD REDEVELOP. BECAUSE THE CIRCULATION HAS BECOME LESS
DEFINED…CONVECTION IS NOT ORGANIZED…SURFACE PRESSURES ARE
RISING AND THE WINDS HAVE DECREASED…ERIKA IS NOW CLASSIFIED AS A
REMNANT LOW…AND COULD DEGENERATE EVEN FURTHER INTO A TROUGH OF
LOW PRESSURE ON FRIDAY. THIS WILL BE THE LAST ADVISORY ON ERIKA
UNLESS REGENERATION OCCUR.
THE REMANT LOW IS MOVING TOWARD THE WEST OR 280 DEGREES AT 6 KNOTS
AND THIS GENERAL MOTION SHOULD CONTINUE ON FRIDAY WITH A GRADUAL
TURN TO THE NORTHWEST. THE REMNANTS OF ERIKA COULD STILL PRODUCE
HEAVY RAINS OVER PORTIONS OF THE LESSER ANTILLES AND PUERTO RICO
DURING THE NEXT DAY OR SO.
FORECAST POSITIONS AND MAX WINDS
INITIAL 04/0300Z 16.8N 65.6W 25 KT…REMNANT LOW
12HR VT 04/1200Z 17.0N 66.5W 25 KT…REMNANT LOW
24HR VT 05/0000Z 18.0N 67.5W 20 KT…REMNANT LOW
36HR VT 05/1200Z 19.5N 68.5W 20 KT…REMNANT LOW
48HR VT 06/0000Z 21.0N 70.0W 20 KT…REMNANT LOW
72HR VT 07/0000Z…DISSIPATED