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Tropical Storm Peter Forecast Discussion Number 2
2021-09-19 10:49:47| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 19 2021 389 WTNT41 KNHC 190849 TCDAT1 Tropical Storm Peter Discussion Number 2 NWS National Hurricane Center Miami FL AL162021 500 AM AST Sun Sep 19 2021 Deep convection has increased since the previous advisory, with the convective cloud pattern having taken on a more curved-band configuration compared to the earlier shear pattern. Satellite intensity estimates from TAFB and SAB support increasing the intensity to 35 kt. In addition, earlier ASCAT passes, which missed the center of circulation, did reveal 30-kt winds west of the center in convection-free areas. Thus, it is reasonable to assume that stronger winds are occurring within the deep convection east of the center, which further supports upgrading the system to Tropical Storm Peter with a 35-kt intensity. The initial estimate is an uncertain 305/13 kt. Peter has made a slight jog to the north-northwest since the previous advisory, but this is likely a short-term motion owing to the center redeveloping farther to the north and east into the deep convection. However, a west-northwestward motion is expected to resume later today. Thereafter, the cyclone is forecast to maintain a west-northwestward motion through Wednesday as Peter moves around the southwestern periphery of a strong deep-layer subtropical ridge. On Thursday and Friday, Peter is forecast to turn northward into a weakness in the ridge induced by the large Post-Tropical Cyclone Odette. The new forecast track has been shifted slightly to the right or north of the previous advisory track, mainly due to the more northward initial position, and lies close to the consensus track models TVCA and HCCA. Some strengthening is forecast during the next 24 hours or so as Peter moves over warmer sea-surface temperatures of about 29 deg C. However, proximity to very dry mid-level air and moderate deep-layer southwesterly vertical wind shear are expected to prevent any significant or rapid strengthening. By early Tuesday and beyond, slow weakening is expected to begin due to increasing wind shear. The new official NHC intensity forecast is very similar to the previous advisory, and closely follows a blend of the IVCN and HCCA intensity consensus models. 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 Sunday into Tuesday across Puerto Rico, the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 18.0N 53.5W 35 KT 40 MPH 12H 19/1800Z 18.8N 55.3W 40 KT 45 MPH 24H 20/0600Z 19.8N 57.8W 40 KT 45 MPH 36H 20/1800Z 20.8N 60.1W 40 KT 45 MPH 48H 21/0600Z 21.7N 62.2W 35 KT 40 MPH 60H 21/1800Z 22.7N 63.9W 35 KT 40 MPH 72H 22/0600Z 23.7N 64.9W 35 KT 40 MPH 96H 23/0600Z 25.8N 65.6W 35 KT 40 MPH 120H 24/0600Z 27.7N 65.2W 35 KT 40 MPH $$ Forecaster Stewart
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