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Tropical Storm Marty Forecast Discussion Number 2
2021-08-23 16:32:46| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Mon Aug 23 2021 000 WTPZ43 KNHC 231432 TCDEP3 Tropical Storm Marty Discussion Number 2 NWS National Hurricane Center Miami FL EP132021 900 AM MDT Mon Aug 23 2021 Marty is now a sheared tropical cyclone owing to northeasterly vertical wind shear of about 15 kt, which has displaced the bulk of the deep convection, with cloud tops colder than -80C, into the western semicircle. The low-level center is estimated be located near the northeastern edge of the sharp convective cloud shield. The initial intensity remains 35 kt based on a subjective Dvorak satellite intensity estimate of T2.5/35 kt from TAFB and an objective estimate of T2.6/37 kt from UW-CIMSS ADT. The initial motion remains westward or 280/13 kt. A strong deep-layer subtropical ridge to the north of Marty is forecast by the global and regional models to remain entrenched across the eastern Pacific basin, keeping Marty moving in a general westward direction for the next couple of days. On days 3 and 4, the ridge is forecast build southward slightly, nudging the cyclone in a west-southwestward direction. The new NHC track forecast is similar to but slightly north, or right, of the previous advisory track, and is also a little south of the tightly packed consensus track models which have shifted northward on this cycle. The moderate northeasterly shear currently affecting Marty is forecast to gradually decrease to 10 kt or less and also become easterly during the next 24-36 hours while the cyclone remains over sea-surface temperatures (SST) of 26 deg C or greater. These favorable conditions should allow for at least slight strengthening during that time. Although the shear is expected to remain low through the remainder of the forecast period, Marty will be moving over sub-26C SSTs and into a drier and more stable airmass. Those unfavorable environmental conditions should combine to erode the central deep convection and weaken the cyclone on days 3 and 4. Marty is forecast to become a depression on Wednesday, degenerate into a remnant low on Thursday, and dissipate on Friday. The official intensity forecast is essentially just an update of the previous NHC forecast, and is about 5 kt above all of the available intensity guidance through 60 hours. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 20.5N 112.4W 35 KT 40 MPH 12H 24/0000Z 20.6N 114.5W 40 KT 45 MPH 24H 24/1200Z 20.6N 117.2W 40 KT 45 MPH 36H 25/0000Z 20.5N 119.3W 35 KT 40 MPH 48H 25/1200Z 20.4N 121.3W 30 KT 35 MPH 60H 26/0000Z 20.3N 123.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/1200Z 20.2N 125.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 27/1200Z 19.3N 130.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 28/1200Z...DISSIPATED $$ Forecaster Stewart
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