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Tropical Storm Rose Forecast Discussion Number 6
2021-09-20 16:47:26| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Sep 20 2021 000 WTNT42 KNHC 201447 TCDAT2 Tropical Storm Rose Discussion Number 6 NWS National Hurricane Center Miami FL AL172021 1100 AM AST Mon Sep 20 2021 While a cursory look at visible satellite images would suggest Rose is intensifying, other data show that it remains a sheared storm. The low- and mid-level centers remain roughly 90 n mi apart according to SSMIS microwave, and a 1038Z ASCAT-A scatterometer pass showed no significant change in intensity overnight. The current wind speed is kept at 35 kt, with a much heavier weight on the 30-kt scatterometer pass than Dvorak estimates near 55 kt. This is a good example of the value of the scatterometer which can tell the forecaster much more about the surface winds that conventional satellite estimates can miss (even if the data is possibly too low with all the thunderstorm activity). There are a lot of thorns in the way of Rose blossoming into a stronger storm. Increasing shear and drier mid-level air are on the way for tonight, competing against the somewhat warm SSTs. Thus Rose has about a day to flower into a moderate tropical storm, and no significant change was made to the short term forecast. At longer range, stronger shear and dry air should pull the petals off Rose one-by-one, causing the cyclone to slowly weaken. The new forecast is similar to the previous one, with some small 5-kt downward adjustments. Rose could even shrivel up into a remnant low by day 5, but that's not shown yet in the forecast. The initial motion remains northwestward at about 14 kt. Rose is still expected to move generally northwestward around the southwestern and western periphery of a strong subtropical ridge during the next few days. Around day 3, however, a mid- to upper-level trough over the north-central Atlantic is forecast to dig southeastward, causing the cyclone to turn northward and eventually northeastward by the weekend. Guidance is in much better agreement on this scenario than the last cycle (though there are still some westward model solutions), and the new NHC track forecast is shifted northeastward at long range. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 17.3N 33.4W 35 KT 40 MPH 12H 21/0000Z 19.0N 34.8W 40 KT 45 MPH 24H 21/1200Z 21.0N 36.1W 35 KT 40 MPH 36H 22/0000Z 22.6N 37.1W 35 KT 40 MPH 48H 22/1200Z 24.1N 38.1W 35 KT 40 MPH 60H 23/0000Z 25.4N 39.1W 30 KT 35 MPH 72H 23/1200Z 26.7N 40.0W 30 KT 35 MPH 96H 24/1200Z 29.0N 40.0W 25 KT 30 MPH 120H 25/1200Z 31.0N 38.0W 25 KT 30 MPH $$ Forecaster Blake
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