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Hurricane Sam Forecast Discussion Number 20
2021-09-27 16:59:08| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Sep 27 2021 759 WTNT43 KNHC 271459 TCDAT3 Hurricane Sam Discussion Number 20 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Mon Sep 27 2021 Sam appeared weaker on satellite images earlier this morning, and the eye was not apparent in visible or infrared satellite imagery. However, a 27/0741 UTC SSMIS pass still showed a well-defined eye. Recent visible and infrared images from the past couple of hours however, show that the structure is becoming better organized again, with the eye again becoming apparent on visible satellite. A NOAA Hurricane Hunter aircraft has made one pass through the hurricane so far and found that the central pressure has risen to about 966 mb. The current intensity estimate is reduced slightly to 110 kt. The aircraft has not yet sampled the northeast quadrant, where the strongest winds are likely occurring. The initial motion is estimated to be northwestward, or 310/7. A subtropical ridge to the north and northeast of Sam will remain the primary steering mechanism over the next several days, and Sam is expected to continue on a similar heading through the next 72 hours or so. A mid- to upper-level trough is forecast to emerge off the U.S. Northeast and Mid-Atlantic coast and dig southward over the western Atlantic late this week. The deep-layer southerly flow ahead of this feature should cause Sam to accelerate to the north-northwest by late Thursday and then turn northward on Friday. The NHC forecast track is largely unchanged from the previous, except it is shifted ever so slightly westward at the hour 72 and 96 points, about midway between the previous NHC forecast and the latest HCCA consensus. The confidence in the track forecast is medium to high through 3 to 4 days. Beyond that time, confidence is about average, as there is some increase in model spread noted. Regarding the intensity forecast, Sam is forecast to travel over warm ocean temperatures while it remains in an environment of low vertical wind shear through the next 4 days. Some mid-level dry air noted on water vapor channels to the west of Sam could play a role in limiting Sam's intensity through hour 48. However, the environment could become more moist again after that time. Due to these competing factors, I opted to hold the intensity steady for the next several days, although fluctuations in intensity can be expected. The NHC intensity forecast is above all model guidance through hour 60, and is in agreement with the model consensus at hour 72-96. After that time, increasing wind shear induced by the approaching mid- to upper-level trough to the northwest of the cyclone should cause weakening. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 15.7N 52.1W 110 KT 125 MPH 12H 28/0000Z 16.4N 52.8W 110 KT 125 MPH 24H 28/1200Z 17.3N 53.9W 110 KT 125 MPH 36H 29/0000Z 18.1N 55.1W 110 KT 125 MPH 48H 29/1200Z 19.1N 56.5W 110 KT 125 MPH 60H 30/0000Z 20.2N 58.1W 110 KT 125 MPH 72H 30/1200Z 21.7N 59.8W 110 KT 125 MPH 96H 01/1200Z 25.9N 62.2W 110 KT 125 MPH 120H 02/1200Z 32.0N 61.3W 100 KT 115 MPH $$ Forecaster Hagen/Pasch
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