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Tropical Storm Karen Forecast Discussion Number 5
2019-09-23 10:56:21| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Sep 23 2019 000 WTNT42 KNHC 230856 TCDAT2 Tropical Storm Karen Discussion Number 5 NWS National Hurricane Center Miami FL AL122019 500 AM AST Mon Sep 23 2019 Karen's convective pattern has become quite disheveled looking this morning due to 20-25 kt of northeasterly vertical wind shear. a narrow band of deep convection has recently reformed in the southeastern quadrant, but proximity to dry air has been hindering development and organization of that convection. The initial intensity has been held at 35 kt until the next reconnaissance flight later this morning provides new information on the strength of the cyclone. However, I would not be surprised if Karen has weakened to a tropical depression based on the lack of significant convection. The initial motion is now 320/07 kt. The track guidance remains in excellent agreement that Karen should continue a northwestward motion today toward a break in the subtropical ridge, followed by a northward motion on Tuesday that would take the center of the cyclone near or over Puerto Rico and the U.S. Virgin Islands in about 36 hours. Karen is forecast to emerge over the southwestern Atlantic near 48 hours and then slow down significantly and possibly even stall or loop several hundred nmi north of Puerto Rico on days 4 and 5 as a large ridge builds to the north of the cyclone. The new NHC track forecast is similar to the previous advisory, and lies close to the average of the consensus track models TVCN, NOAA-HCCA, and FSSE. The upper-level winds are expected to remain unfavorable for the next 24 hours or so, and I would not be surprised if Karen weakens to a tropical depression during that time. By 36 hours and beyond, however, upper-level winds are expected to become much less hostile, allowing some modest strengthening to occur. By days 4 and 5, Karen is forecast to move underneath an upper-level anticyclone, which should allow for more significant intensification to occur. The new official intensity forecast is similar to the previous one, and follows the trend of the various intensity consensus models. Key Messages: 1. Heavy rainfall will continue to affect portions of the southern Windward Islands through tonight. 2. Karen is forecast to approach Puerto Rico, and the U.S. and British Virgin Islands on Tuesday, and a tropical storm watch is in effect. Tropical-storm-force winds, heavy rainfall, and flash flooding are possible on these islands. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 13.6N 63.9W 35 KT 40 MPH 12H 23/1800Z 14.5N 64.6W 35 KT 40 MPH 24H 24/0600Z 16.1N 65.2W 35 KT 40 MPH 36H 24/1800Z 18.0N 65.6W 35 KT 40 MPH 48H 25/0600Z 20.1N 65.5W 40 KT 45 MPH 72H 26/0600Z 24.6N 64.9W 45 KT 50 MPH 96H 27/0600Z 26.5N 65.5W 50 KT 60 MPH 120H 28/0600Z 27.0N 67.0W 60 KT 70 MPH $$ Forecaster Stewart
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