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Hurricane Maria Forecast Discussion Number 18
2017-09-20 16:40:55| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 20 2017 000 WTNT45 KNHC 201440 TCDAT5 Hurricane Maria Discussion Number 18 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Wed Sep 20 2017 The last radar image from the San Juan WSR-88D was received at 0950 UTC when Maria's eye was located only about 5 n mi off the southeastern coast of Puerto Rico. Subsequent 1-minute imagery from the GOES-16 satellite, as well as surface observations, indicate that the eye made landfall a little south of Yabucoa Harbor, Puerto Rico, around 1015 UTC. Now that the center is moving over the mountainous terrain of the island, the eye has become cloud filled, and the infrared satellite presentation has degraded. Without radar velocity data, the initial intensity is incredibly uncertain, but my best guess is 120 kt based on a typical inland decay rate. Maria's center is expected to move off the northern coast of Puerto Rico soon, and an Air Force Reserve reconnaissance aircraft is scheduled to intercept the center early this afternoon and provide a better estimate of how much Maria has weakened. The initial motion is northwestward, or 305/10 kt. This northwestward motion is forecast to continue for the next 48 hours, followed by a turn toward the north by days 4 and 5, while Maria moves between a mid-level high centered southeast of Bermuda and a broad trough extending from Tropical Storm Jose southwestward into the Gulf of Mexico. The track guidance is tightly clustered this cycle, and there were no significant changes made to the NHC forecast track. Once Maria moves off the coast of Puerto Rico, it will take some time for the structure to reorganize over the warm waters of the Atlantic Ocean. However, the shear is expected to be less than 10 kt for the next 24-36 hours, and Maria has an opportunity to restrengthen a bit over that time period. After 36 hours, a gradual increase in shear is likely to lead to a commensurate gradual decrease in the hurricane's intensity through the end of the forecast period. Since the SHIPS model, in particular, responds to the favorable conditions for intensification, the NHC intensity forecast lies just above the intensity consensus through much of the forecast period. Since we don't have radar imagery from San Juan, and the eye has become cloud filled in satellite imagery, the hourly position updates are being discontinued. KEY MESSAGES: 1. Maria's core is moving over Puerto Rico, with life-threatening wind, storm surge, and rainfall impacts continuing over the island. Everyone in Puerto Rico should follow advice from local officials to avoid life-threatening flooding from storm surge and rainfall. A Hurricane Warning remains in effect for the Virgin Islands, but conditions should gradually improve there later today. 2. Wind speeds atop and on the windward sides of hills and mountains and on high-rise buildings could be much stronger than the near-surface winds indicated in this advisory. 3. A Hurricane Warning is also in effect for the northern coast of the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas, where Maria is expected to bring dangerous wind, storm surge, and heavy rainfall. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 18.4N 66.5W 120 KT 140 MPH...OVER PUERTO RICO 12H 21/0000Z 19.2N 67.6W 120 KT 140 MPH 24H 21/1200Z 20.2N 69.0W 125 KT 145 MPH 36H 22/0000Z 21.2N 70.1W 125 KT 145 MPH 48H 22/1200Z 22.4N 71.0W 120 KT 140 MPH 72H 23/1200Z 25.3N 72.4W 110 KT 125 MPH 96H 24/1200Z 28.5N 73.0W 100 KT 115 MPH 120H 25/1200Z 31.5N 73.0W 90 KT 105 MPH $$ Forecaster Berg
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