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Tropical Storm Peter Forecast Discussion Number 5
2021-09-19 22:40:06| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 19 2021 000 WTNT41 KNHC 192039 TCDAT1 Tropical Storm Peter Discussion Number 5 NWS National Hurricane Center Miami FL AL162021 500 PM AST Sun Sep 19 2021 Over the past few hours deep convection with cloud tops as cold as -85 degrees C have developed near and to the east of the center of Peter. An Air Force Reserve Hurricane Hunter aircraft investigating the system earlier provided data during several legs of the flight that confirmed an intensity of 40 kt. A blend of the latest Dvorak T- and CI- numbers from TAFB are consistent with that data, and therefore the initial intensity remains 40 kt for this advisory. The vertical wind shear that stripped Peter of its deep convection earlier today is forecast to increase further through tonight and persist for at least a few days. Global model simulated satellite imagery suggests this latest burst of convection will also become removed from the center within several hours, with the cyclone struggling to maintain persistent deep convection throughout much of the 5-day forecast period. Therefore, despite being over very warm waters, Peter is forecast to slowly weaken over the next several days. The intensity model guidance is in decent agreement on this scenario, and the NHC forecast remains near the various intensity consensus solutions. As mentioned in the previous discussion, there are some indications, particularly by the GFS, that Peter could open back into a wave within a few days which adds some additional uncertainty to the intensity forecast. Peter's initial motion remains 290/15 kt. The storm is forecast to continue to move in this west-northwestward direction for the next couple of days as it is steered to the south of a subtropical ridge. This ridge is expected to weaken in a few days which should cause the cyclone to slow its forward motion and turn northwestward. Late in the forecast period a turn to the north and possibly northeast is expected to occur as Peter gets caught in the flow around a large trough to its north. The model guidance has shifted westward beyond day 2, in part due to a faster forward motion. While the timing of the cyclone's turn to the north remains the same, the NHC forecast was shifted to the left beyond 48 h, but still remains to the east of the consensus. Based on the track, intensity, and wind radii forecast, no tropical storm watches or warnings are required for the northern Leeward Islands, Virgin Islands or Puerto Rico. However, interests there should monitor the progress of the system as locally heavy rain is possible on Monday and Tuesday when it is expected to pass to the north of the area. Key Messages: 1. Rainfall around the southern periphery of Tropical Storm Peter may lead to areas of urban and small stream flooding from late today into Tuesday across Puerto Rico, the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 18.4N 57.8W 40 KT 45 MPH 12H 20/0600Z 19.1N 59.8W 40 KT 45 MPH 24H 20/1800Z 19.9N 62.1W 35 KT 40 MPH 36H 21/0600Z 20.8N 64.3W 35 KT 40 MPH 48H 21/1800Z 21.9N 66.0W 35 KT 40 MPH 60H 22/0600Z 22.9N 67.2W 35 KT 40 MPH 72H 22/1800Z 24.1N 68.2W 30 KT 35 MPH 96H 23/1800Z 26.1N 68.3W 30 KT 35 MPH 120H 24/1800Z 27.7N 67.5W 30 KT 35 MPH $$ Forecaster Latto
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