000 WTNT45 KNHC 172053 TCDAT5 Hurricane Maria Discussion Number 6 NWS National Hurricane Center Miami FL AL152017 500 PM AST Sun Sep 17 2017 A burst of deep convection developed over Maria's center since the last advisory and has continued to expand in size. The Air Force Hurricane Hunter aircraft investigating the cyclone found maximum flight-level winds of 63 kt and SFMR surface winds of 64 kt. The crew also noted the formation of an open eyewall. Based on these data and observations, Maria is upgraded to a 65-kt hurricane. The initial motion remains west-northwestward, or 283/13 kt. Maria is expected to maintain this trajectory for quite some time, but it will likely slow down during the next 36 hours as it approaches the Lesser Antilles. Overall, the track guidance is tightly clustered for the entire 5-day forecast period, which increases confidence in the NHC track forecast. The updated official forecast is slightly south of the previous one for the first 36 hours, mainly due to the update of the initial position found by the aircraft, but it is right along the previous track after 36 hours. This solution is between the GFS and ECMWF models and very close to the HCCA solution. The aircraft data indicate that Maria has a compact circulation, which could make it a prime candidate for significant intensification in an environment of low shear and warm SSTs. Rapid intensification indices are not especially high, but nonetheless, Maria is forecast to continue strengthening and potentially reach major hurricane by 48 hours. If that occurs, some fluctuations in intensity could occur due to eyewall replacements and land interaction, but Maria will likely remain as a major hurricane on days 3 through 5. Because of Maria's small size the chance of significant strengthening is higher, and the NHC intensity forecast is near the high end of the guidance, closest to the HWRF and HCCA models. KEY MESSAGES: 1. Maria has strengthened to a hurricane and could be near major hurricane intensity when it affects portions of the Leeward Islands over the next few days, bringing dangerous wind, storm surge and rainfall hazards. Hurricane and tropical storm warnings have been issued for portions of the Leeward Islands, and these warnings will likely be extended northward and westward tonight or on Monday. 2. Maria is likely to affect the British and U.S. Virgin Islands and Puerto Rico by mid week as a dangerous major hurricane. Hurricane watches have been issued for the U.S. and British Virgin Islands and could be extended to Puerto Rico tonight or early Monday. Interests in these areas should monitor the progress of Maria and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 13.8N 57.5W 65 KT 75 MPH 12H 18/0600Z 14.3N 59.0W 75 KT 85 MPH 24H 18/1800Z 15.1N 60.5W 85 KT 100 MPH 36H 19/0600Z 15.8N 61.8W 95 KT 110 MPH 48H 19/1800Z 16.5N 63.1W 105 KT 120 MPH 72H 20/1800Z 17.8N 65.8W 110 KT 125 MPH 96H 21/1800Z 19.0N 68.5W 110 KT 125 MPH 120H 22/1800Z 21.0N 71.0W 105 KT 120 MPH $$ Forecaster Berg