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Tropical Storm Theta Forecast Discussion Number 13
2020-11-13 03:52:52| National Hurricane Center (Atlantic)
Issued at 300 AM GMT Fri Nov 13 2020 121 WTNT45 KNHC 130252 TCDAT5 Tropical Storm Theta Discussion Number 13 NWS National Hurricane Center Miami FL AL302020 300 AM GMT Fri Nov 13 2020 The structure of Theta has been waxing and waning today with moderate convection attempting to wrap around the center, though the coldest cloud tops have been decaying before wrapping fully around. Earlier, there was a 2222 UTC partial ASCAT-B pass that showed peak winds of 40-45 kt on the south side of Theta. However the highest winds from this instrument the previous two nights were in the southwest quadrant and it is estimated that higher winds may still exist in this quadrant of Theta. For this reason, the latest intensity estimate is only adjusted downward to 50 kt for this advisory. Theta continues to track east at 090/12 kt as the system remains steered by flow along the north side of a mid-level ridge. This ridge is forecast to gradually weaken over the next 24-36 h and Theta is forecast to bend to the east-southeast as the cyclone becomes more influenced by mid-level northerly flow associated with an upstream ridge building to the northwest. After 36 h, Theta is expected to slow down significantly as it becomes a shallow cyclone in light low-level flow. Finally, low-level southerly flow ahead of a mid-latitude cyclone is forecast to steer Theta's remnant low northeastward by the end of the forecast. The track guidance this cycle has shifted a bit southward for the first part of the forecast, and the official NHC track forecast has been adjusted slightly further south, close to the reliable ICVN consensus. Thus far, Theta has been struggling to produce deep convection that has successfully wrapped around its center. While Vertical Wind Shear is forecast to decrease per ECMWF-SHIPS guidance over the next 12-24 h, it remains to be seen if the current degree of instability is enough for Theta to take advantage of the more conducive wind environment. Thereafter, Vertical Wind Shear increases sharply from the north, importing a much more stable environment over Theta. For now, the latest NHC intensity forecast maintains the current 50 kt intensity over the next 24 h with weakening forecasted thereafter, in general agreement with the latest intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 31.7N 26.0W 50 KT 60 MPH 12H 13/1200Z 31.7N 24.2W 50 KT 60 MPH 24H 14/0000Z 31.4N 22.1W 50 KT 60 MPH 36H 14/1200Z 31.0N 20.4W 45 KT 50 MPH 48H 15/0000Z 30.8N 19.2W 40 KT 45 MPH 60H 15/1200Z 30.8N 18.6W 30 KT 35 MPH 72H 16/0000Z 31.2N 18.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 17/0000Z 34.3N 18.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 18/0000Z...DISSIPATED $$ Forecaster Papin/Cangialosi
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