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Tropical Depression Thirteen-E Forecast Discussion Number 1
2020-08-26 10:49:50| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Aug 26 2020 000 WTPZ43 KNHC 260849 TCDEP3 Tropical Depression Thirteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP132020 300 AM MDT Wed Aug 26 2020 The broad area of low pressure that the NHC has been tracking the past few days has become better defined based on a 0356Z ASCAT-B scatterometer overpass. Although the system is slightly elongated northeast-to-southwest, the center is well defined and deep convection has persisted west of the center despite strong easterly vertical wind shear of 25-30 kt. Thus, the low has been upgraded to Tropical Depression 13-E. The initial intensity of 30 kt is based on scatterometer surface wind speeds of 30-32 kt, which are consistent with T2.0/30-kt satellite classifications from TAFB-SAB. The initial motion estimate is slowly north-northeastward or 025/04 kt. The depression is embedded within an east-to-west oriented cyclonic gyre with a high-amplitude mid-level ridge located over the southwestern U.S. and northern Mexico. These gyre will cause the cyclone to move slowly northward today and northwestward on Thursday, with the ridge acting as a poleward block and forcing to system to turn west-northwestward to westward on Friday and Saturday. On the forecast track, the cyclone is expected to remain just offshore the southwestern coast of Mexico today and Thursday, and pass near or just south of the southern tip of Baja California Sur on Friday and Saturday. The NHC official track forecast closely follows the simple consensus model TVCE, and lies a little to the left or west of the corrected-consensus model HCCA and the ECMWF model tracks. Strong easterly shear is forecast to persist through the next 24 hours, so little if any strengthening is expected during that time. In fact, convection is likely to erode a little during the day today, and then redevelop closer to the center tonight when the shear begins to abate somewhat. In the 36-60 hour period, the shear is forecast to weaken considerably from the northeast, allowing for some slight strengthening to occur. However, the intensity is not expected to increase to more than 35-40 kt, with the strongest winds and heaviest rains remaining offshore the southwestern coast of Mexico. For those reason, a tropical warning has not been issued for southwestern Mexico at this time. The official intensity forecast follows a blend of the HCCA, HWRF, and ECMWF models intensity forecasts. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 17.5N 106.7W 30 KT 35 MPH 12H 26/1800Z 18.1N 106.3W 30 KT 35 MPH 24H 27/0600Z 19.0N 106.3W 35 KT 40 MPH 36H 27/1800Z 20.1N 107.0W 35 KT 40 MPH 48H 28/0600Z 21.3N 108.1W 35 KT 40 MPH 60H 28/1800Z 22.3N 109.4W 35 KT 40 MPH 72H 29/0600Z 23.3N 111.3W 30 KT 35 MPH 96H 30/0600Z 23.3N 114.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 31/0600Z 22.7N 115.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart
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