Tropical Depression Eighteen Discussion Number 2
Statement as of 5:00 am EDT on September 18, 2005 the reconaissance aircraft that was en Route to Tropical Storm Philippe was diverted to the depression...and we very much appreciate the last minute flexibility of the aircrew. When they first got to the depression...they didn't find much...including only 5 kt of west wind and a center southwest of the deep convection. However...on their second pass through they found that the center had migrated or redeveloped closer to the convection... which is now taking on a slightly more banded appearance on the first few images after the satellite eclipse. These observations suggest that the depression is becoming better organized. The peak flight-level winds were 36 kt...which supports an initial intensity estimate of 25 kt. The aircraft data require a relocation of the center to the south and west of the previous track...and this results in a slight southward shift of the official forecast. However...the basic track reasoning remains the same. The depression is expected to move west-northwestward for the next couple of days toward a weakness in the subtropical ridge just east of Florida. After that...high pressure over Texas and the western Gulf should turn the depression westward. The official forecast is in best agreement with the GFS and GFDL guidance. The UKMET is farther south...taking the cyclone across central and western Cuba. The Canadian model is also south of its previous track...taking the center just south of Key West. Upper-level low pressure is centered over central Cuba...and this low is producing some southerly shear over the depression. This should limit intensification in the short term...however...this low is forecast by all the global models to weaken and be replaced by a narrow ridge of high pressure over the next two to three days. This upper pattern...coupled with very warm sea surface temperatures along the path of the cyclone...would favor more rapid development as long as the cyclone avoids the land mass of Cuba. The GFDL is not nearly as agressive as it was earlier today...not making the system a hurricane until it is well into the Gulf of Mexico. The official forecast is a little slower than the previous advisory in bringing the system to hurricane strength and follows a blend of the SHIPS and GFDL guidance. Forecaster Franklin forecast positions and Max winds initial 18/0900z 21.7n 71.2w 25 kt 12hr VT 18/1800z 22.2n 73.0w 30 kt 24hr VT 19/0600z 22.8n 75.3w 35 kt 36hr VT 19/1800z 23.4n 77.5w 45 kt 48hr VT 20/0600z 23.8n 80.0w 55 kt 72hr VT 21/0600z 24.0n 84.5w 65 kt 96hr VT 22/0600z 24.0n 89.5w 75 kt 120hr VT 23/0600z 24.0n 93.5w 80 kt
Tropical Depression Eighteen Advisory Number 2
Statement as of 5:00 am EDT on September 18, 2005 ...Depression organizing east of the Bahamas... A Tropical Storm Warning remains in effect for the Turks and Caicos Islands...and for the southeast and central Bahamas. A Tropical Storm Warning means that tropical storm conditions are expected within the warning area within the next 24 hours. A Hurricane Watch remains in effect for the northwest Bahamas. A Hurricane Watch means that hurricane conditions are possible within the watch area...generally within 36 hours. Interests in South Florida...the Florida Keys...as well as central and western Cuba should closely monitor the progress of this system. For storm information specific to your area...including possible inland watches and warnings...please monitor products issued by your local weather office. At 5 am EDT...0900z...the center of Tropical Depression Eighteen was re-located near latitude 21.7 north... longitude 71.2 west or about 15 miles... 25 km... north-northwest of Grand Turk island and about 455 miles... 730 km...east-southeast of Nassau. The depression is moving toward the west near 12 mph ...19 km/hr. A general motion toward the west-northwest is expected over the next 24 hours. Maximum sustained winds are near 30 mph... 45 km/hr...with higher gusts. The depression is expected to become a tropical storm during the next day or so. The latest minimum central pressure reported by reconaissance aircraft was 1008 mb...29.77 inches. The depression is expected to produce total rainfall accumulations of 3 to 5 inches over much of the turks and caicos...and over the southeast and central Bahamas...with possible isolated maximum amounts of 8 inches. Repeating the 5 am EDT position...21.7 N... 71.2 W. Movement toward...west near 12 mph. Maximum sustained winds... 30 mph. Minimum central pressure...1008 mb. An intermediate advisory will be issued by the National Hurricane Center at 8 am EDT followed by the next complete advisory at 11 am EDT. Forecaster Franklin