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Tropical Depression EIGHT-E Forecast Discussion Number 1
2015-07-27 22:55:24| National Hurricane Center (East Pacific)
Issued at 200 PM PDT MON JUL 27 2015 000 WTPZ43 KNHC 272055 TCDEP3 TROPICAL DEPRESSION EIGHT-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082015 200 PM PDT MON JUL 27 2015 The low pressure system located more than 1000 n mi west-southwest of the Baja California peninsula has finally acquired enough persistent deep convection near the center for it to be upgraded to a tropical depression. An 1831 UTC ASCAT-B overpass indicated a well-defined circulation center and inner-core wind field containing several 30-31 kt surface wind vectors at a distance of 35-40 nmi to the northeast and southeast of the center. Although the depression is a sheared tropical cyclone, a T2.0/30 kt Dvorak satellite classification from TAFB also justifies upgrading the low to a tropical depression at this time. The initial motion estimate is 290/14 kt, which is based primarily on microwave and ASCAT satellite fixes. The NHC model guidance is in good agreement on the tropical cyclone moving toward the west-northwest at 12-14 kt for the next 72 hours or so due to a strong deep-layer ridge locate to its north. After that, however, the guidance diverges significantly with the ECMWF model taking a very weak cyclone or trough west-southwestward, the GFS and HWRF models moving the system westward, while the GFS-ensemble mean and the remainder of the models keep the depression on a slower west-northwestward track. The NHC official forecast track basically lies down the middle of the guidance suite throughout the forecast period and is close to the consensus model TVCE. The cyclone is not expected to intensify much due to persistent moderate northwesterly vertical wind shear and the cyclone moving over marginal sea-surface temperatures after 72 hours. There will also likely be occasional intrusions of drier and more stable air, which lies just to the north of the forecast track, into the cyclone. However, the well-established southerly low-level inflow of unstable air should help to maintain enough convection to keep this system as a tropical cyclone throughout the forecast period. The NHC intensity forecast is similar to the ICON consensus model. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 15.6N 126.1W 30 KT 35 MPH 12H 28/0600Z 16.1N 128.1W 30 KT 35 MPH 24H 28/1800Z 16.6N 130.4W 35 KT 40 MPH 36H 29/0600Z 17.0N 132.6W 35 KT 40 MPH 48H 29/1800Z 17.3N 134.6W 35 KT 40 MPH 72H 30/1800Z 17.9N 139.8W 35 KT 40 MPH 96H 31/1800Z 18.2N 145.9W 35 KT 40 MPH 120H 01/1800Z 18.4N 151.3W 30 KT 35 MPH $$ Forecaster Stewart
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