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#799393 (Received by flhurricane at: 1:50 AM 30.Aug.2015) TCDAT1 TROPICAL DEPRESSION SIX SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 130 AM AST SUN AUG 30 2015 The well-defined low pressure system located to the west of Conakry, Guinea, has acquired sufficient organized convection to be classified as a tropical depression. The initial intensity of 30 kt is based on a Dvorak satellite intensity estimate of T2.0/30 kt from TAFB and two earlier ASCAT scatterometer passes indicating at least 30 kt in the southern semicircle. The initial motion estimate is 305/10 kt. The depression is located south of a deep-layer subtropical ridge that extends westward across northwestern Africa and into the eastern Atlantic for several hundred miles. However, a weakness is located in a portion of the ridge to the north of the Cape Verde Islands due to a pronounced mid-latitude trough noted in water vapor imagery digging east-southeastward. This should allow the cyclone to move northwestward toward the Cape Verde Islands through 48 hours. After that time, the NHC model guidance is in fair agreement on the aforementioned trough lifting out, allowing the ridge to build back in, which is expected to force the cyclone on a more westward track. The NHC track forecast lies close to the consensus models TVCA and GFEX. The depression is embedded within favorable environmental and oceanic conditions consisting of low vertical wind shear of less than 10 kt, a moist mid-troposphere, and sea-surface temperatures greater than 28 deg C, which should allow for steady strengthening for the next 48 hours or so. The main inhibiting factor is the decreasing instability ahead of the cyclone after 24-36 hours. However, the possibility still exists for the system to reach hurricane status before or while it moves through the Cape Verde Islands in 36-48 hours. For this reason, the Meteorological Service of the Cape Verde Islands has issued a Hurricane Watch and a Tropical Storm Warning for all of the Cape Verdes. The official intensity forecast is basically a blend of the SHIPS and LGEM models. FORECAST POSITIONS AND MAX WINDS INIT 30/0530Z 12.1N 18.4W 30 KT 35 MPH 12H 30/1200Z 12.7N 19.5W 35 KT 40 MPH 24H 31/0000Z 13.9N 21.2W 45 KT 50 MPH 36H 31/1200Z 15.3N 23.1W 55 KT 65 MPH 48H 01/0000Z 16.6N 24.9W 60 KT 70 MPH 72H 02/0000Z 18.3N 29.0W 60 KT 70 MPH 96H 03/0000Z 18.9N 32.9W 55 KT 65 MPH 120H 04/0000Z 19.3N 36.8W 50 KT 60 MPH $$ Forecaster Stewart |