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Tropical Storm Norbert Forecast Discussion Number 7
2020-10-07 10:48:12| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Oct 07 2020 000 WTPZ44 KNHC 070848 TCDEP4 Tropical Storm Norbert Discussion Number 7 NWS National Hurricane Center Miami FL EP192020 300 AM MDT Wed Oct 07 2020 Norbert has weakened as entrainment of dry air has disrupted the compact system. The center was partially exposed overnight, but recent infrared imagery shows a new burst of deep convection near the center. Microwave imagery and ASCAT scatterometer wind data indicated the center had drifted southwest from its previous position, as the storm is beginning to meander within the weak steering flow. The initial intensity has been lowered to 35 kt based on the recent ASCAT-A overpass that showed a peak wind of 33 kt, as well as a T2.5 Dvorak estimate from TAFB. The intensity forecast for Norbert remains tricky given its small circulation and the presence of dry air in the surrounding environment. Sea-surface temperatures are more than sufficient for at least modest strengthening, but the question will be whether Norbert can survive the increased southeasterly shear that the SHIPS guidance calls for during the next 24-48 h. If so, Norbert may remain a tropical storm through the next 5 days. Alternatively, the shear and additional bouts of dry air entrainment could weaken the system to a depression or even a remnant low late in the forecast period. While small intensity changes due to diurnal fluctuations in convection are certainly possible, the official NHC forecast keeps Norbert's intensity forecast at 35 kt in consideration of the mixed signals noted in the latest intensity guidance. As previously mentioned, the center of Norbert has drifted to the southwest overnight. The storm is expected to remain nearly stationary over the next couple of days as distant Hurricane Delta over the northwestern Caribbean Sea has weakened the ridge that had been steering Norbert. Therefore, the forecast track through 48 h is more uncertain than usual given the potential for erratic motion as indicated by the diverging model solutions. By Friday, Norbert should begin moving slowly westward or west-northwestward as the ridge gradually builds to the north. The NHC track forecast remains fairly close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 14.0N 107.1W 35 KT 40 MPH 12H 07/1800Z 13.9N 107.2W 35 KT 40 MPH 24H 08/0600Z 13.9N 107.3W 35 KT 40 MPH 36H 08/1800Z 14.0N 107.6W 35 KT 40 MPH 48H 09/0600Z 14.0N 108.0W 35 KT 40 MPH 60H 09/1800Z 14.1N 108.7W 35 KT 40 MPH 72H 10/0600Z 14.6N 109.5W 35 KT 40 MPH 96H 11/0600Z 15.5N 111.0W 35 KT 40 MPH 120H 12/0600Z 16.5N 112.5W 35 KT 40 MPH $$ Forecaster Reinhart/Stewart
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