000 WTNT43 KNHC 012034 TCDAT3 Hurricane Sam Discussion Number 37 NWS National Hurricane Center Miami FL AL182021 500 PM AST Fri Oct 01 2021 Sam remains a powerful hurricane. The eye is still very distinct and there are several mesovorticies evident in satellite imagery. In addition, microwave images show a closed and symmetric eyewall. Data from the Air Force Hurricane Hunters indicate that Sam has been maintaining its category 4 intensity. The aircraft measured peak flight-level winds at 700 mb of 152 kt, which corresponds to a 135-140 kt surface wind. However, the peak SFMR winds are around 115 kt. Dropsonde data from the aircraft show a sharp decrease in winds around the 925 mb level, which could mean that the strongest winds are not reaching the surface. The minimum pressure in the eye remains very low though at 937 mb. Based on all of this data, the initial intensity is held at 130 kt, but there is some uncertainty in that estimate. The major hurricane continues northward and the latest initial motion estimate is 355/17 kt. The large-scale pattern consists of a deep-layer ridge to the northeast of Sam and a large low pressure system centered over Atlantic Canada. The steering flow between these features should cause Sam to move northeastward at a sightly slower pace this weekend. By early next week, the deep-layer low is expected to retreat northward, which should cause Sam to turn a little more to the right. The models are in fairly good agreement, but there are some notable speed differences with the UKMET on the faster side and the GFS on the slower side of the guidance envelope. No major changes were made to the NHC track forecast, and it remains near the consensus aids. Sam is expected to slowly weaken during the next several days as it moves over progressively cooler waters and into an environment of stronger shear. The hurricane will likely begin extratropical transition in a couple of days when it crosses the 26 degree C isotherm, and this transition is expected to be completed shortly after 72 hours. All of the model guidance shows steady weakening through the forecast period, and so does the NHC forecast. This prediction is close to the IVCN, IVDR, and HCCA models in the short term and near the GFS model during the extratropical portion of the forecast. Even though Sam is likely to weaken, it is still expected to be a significant storm over the next several days. Key Messages: 1. Swells generated by Sam will impact the northern Leeward Islands the Greater Antilles, the Bahamas, and Bermuda during the next couple of days. Swells are expected to reach the United States east coast and Atlantic Canada on Saturday. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. Tropical storm conditions are possible on Bermuda beginning tonight or early Saturday, and a Tropical Storm Warning is in effect for the island. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 30.0N 61.8W 130 KT 150 MPH 12H 02/0600Z 32.3N 61.0W 120 KT 140 MPH 24H 02/1800Z 34.8N 59.4W 110 KT 125 MPH 36H 03/0600Z 36.7N 57.3W 100 KT 115 MPH 48H 03/1800Z 38.6N 54.2W 95 KT 110 MPH 60H 04/0600Z 41.1N 50.1W 90 KT 105 MPH 72H 04/1800Z 44.9N 45.6W 85 KT 100 MPH 96H 05/1800Z 50.5N 40.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 06/1800Z 52.6N 30.7W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi/Nepaul