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Tropical Depression FIFTEEN-E Forecast Discussion Number 1
2014-09-10 10:47:05| National Hurricane Center (East Pacific)
Issued at 200 AM PDT WED SEP 10 2014 000 WTPZ45 KNHC 100846 TCDEP5 TROPICAL DEPRESSION FIFTEEN-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152014 200 AM PDT WED SEP 10 2014 Deep convection has increased in association with the area of low pressure located southwest of Acapulco, and the system is now designated a tropical depression. The convective pattern consists of a large area of tops colder than -80C west of the center and some curved bands forming to the north. The initial intensity of 30 kt is based on data from a pair of ASCAT passes between 0300 and 0500 UTC. The SHIPS model shows moderate easterly to northeasterly shear over the cyclone, consistent with the location of the low-level center on the eastern edge of the convective canopy as shown by the ASCAT data. The shear should continue for the next 24 to 36 hours, which should result in gradual strengthening as the cyclone is situated over very warm SSTs around 30C. By 48 hours, the shear is expected to decrease, allowing the cyclone to take better advantage of the favorable oceanic conditions and intensify more quickly. There is considerable spread in the intensity guidance. The SHIPS model is the most aggressive, showing the system reaching 90 kt by 72 hours. The HWRF shows quick strengthening in the short term, but then weakens the cyclone due to land interaction. The GFDL model also shows land interaction and a weaker solution. Given that the NHC track keeps the center offshore, the official intensity forecast will be above the intensity consensus but below the SHIPS model, showing the cyclone reaching 70 kt in 72 hours and peaking at 80 kt at days 4 and 5. The initial motion is a north-northwestward drift, as the depression is situated in a region of weak steering south of a mid-level ridge. The western part of the ridge will gradually erode over the next 48 to 72 hours, which should allow the deepening cyclone to begin moving slowly northwestward to north-northwestward. Later in the period, the cyclone should accelerate northwestward as the ridge strengthens to the east. While overall the guidance is in general agreement on this scenario, there are significant detail differences that will determine how close the system comes to the coast of southwestern Mexico in 72 to 96 hours. The ECMWF shows more interaction with an upper-low retrograding westward across Mexico and pulls the cyclone farther to the east and closer to the coast. On the other hand, the GFS has a track farther offshore showing less influence from the upper-level low and more interaction with the disturbance currently situated about 1,000 miles west-southwest of the depression. The NHC forecast is close to a blend of the GFS and ECMWF models through the period and is a little slower than and left of the TVCE consensus at days 4 and 5. Given the present weak steering currents and and spread of the model guidance, confidence in the details of the track forecast is lower than usual. A tropical storm watch may be needed for a portion of the coast of southwestern Mexico later today. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 14.4N 102.5W 30 KT 35 MPH 12H 10/1800Z 14.5N 102.5W 40 KT 45 MPH 24H 11/0600Z 14.7N 102.6W 45 KT 50 MPH 36H 11/1800Z 15.0N 102.7W 50 KT 60 MPH 48H 12/0600Z 15.4N 102.8W 60 KT 70 MPH 72H 13/0600Z 16.9N 103.6W 70 KT 80 MPH 96H 14/0600Z 20.0N 106.5W 80 KT 90 MPH 120H 15/0600Z 23.0N 109.5W 80 KT 90 MPH $$ Forecaster Brennan
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