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Tropical Storm Peter Forecast Discussion Number 8
2021-09-20 16:44:53| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Sep 20 2021 000 WTNT41 KNHC 201444 TCDAT1 Tropical Storm Peter Discussion Number 8 NWS National Hurricane Center Miami FL AL162021 1100 AM AST Mon Sep 20 2021 West-southwesterly vertical wind shear on the order of 30 kt is pummeling Peter this morning. Just like yesterday morning, the low-level center of the storm is pulling away from the deep convection and is now displaced greater than 80 n mi. An Air Force Reserve Hurricane Hunter aircraft has been investigating Peter this morning and has measured peak 925-mb flight-level winds of 54 kt and several SFMR values of 40-45 kt, supporting keeping the initial intensity at 45 kt for this advisory. Peter refuses to slow down, and for the past several hours has been moving 290/14 kt. This west-northwestward motion is forecast to continue for the next two days as the system remains to the southwest of a subtropical ridge. By Wednesday, Peter should slow down and turn northwest then north as it reaches a developing weakness in the ridge carved out by a mid-latitude trough moving across the northeastern United States later this week. The model track guidance has shifted slightly left for the 24-72 h time frames, and the NHC forecast track was nudged in that direction as well. Otherwise, the latest NHC forecast track is little changed from the previous one. An upper-level trough to the west of Peter is forecast to remain near the cyclone for the next few days, keeping the storm in a high-shear environment. Therefore, despite being over warm waters the storm is forecast to slowly weaken. If Peter survives the next 72 h, there could be a window of opportunity late in the forecast period for some modest strengthening as the cyclone would have lifted to the north of the upper trough. It should be noted that a vast majority of the GFS ensembles show Peter dissipating later this week as the system opens into a wave. This scenario is plausible, especially if deep convection fails to persist near the center of the cyclone. The latest NHC intensity forecast assumes Peter survives, and closely follows the various intensity consensus solutions. Based on the latest track, intensity, and wind radii forecasts, no tropical storm watches or warnings are required for the northern Leeward Islands, Virgin Islands, or Puerto Rico at this time. However, locally heavy rain is possible today and Tuesday when Peter is expected to pass to the north of these locations. Key Messages: 1. Rainfall around the southern periphery of Tropical Storm Peter may lead to areas of urban and small stream flooding through Tuesday across northern Hispaniola, Puerto Rico, the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 19.5N 60.9W 45 KT 50 MPH 12H 21/0000Z 20.1N 62.7W 40 KT 45 MPH 24H 21/1200Z 20.8N 64.8W 40 KT 45 MPH 36H 22/0000Z 21.8N 66.6W 35 KT 40 MPH 48H 22/1200Z 22.7N 67.9W 35 KT 40 MPH 60H 23/0000Z 23.5N 68.6W 30 KT 35 MPH 72H 23/1200Z 24.5N 68.7W 30 KT 35 MPH 96H 24/1200Z 26.5N 67.6W 30 KT 35 MPH 120H 25/1200Z 28.6N 66.4W 35 KT 40 MPH $$ Forecaster Latto
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