| Track: https://www.nhc.noaa.gov/refresh/graphics_at3+shtml/?cone#contents Satellite floater: https://www.star.nesdis.noaa.gov/GOES/floater.php?stormid=AL082021 Tropical Storm Henri Discussion Number 18 NWS National Hurricane Center Miami FL AL082021 500 AM EDT Fri Aug 20 2021 Henri's low-level center has been peaking out from under the north side of the deep convective mass, resulting from continued 20-25 kt of northerly shear. Maximum winds are still estimated to be 55 kt based on T3.5 Dvorak estimates from TAFB and SAB. Henri still has a motion toward the west-northwest, or 300/8 kt, but it is about ready to make the sharp right turn that we've been expecting. A shortwave trough currently over the central Appalachians is forecast to close off by Saturday, with Henri accelerating northward on the east side of this feature through the weekend. Some global models show Henri merging with the mid-/upper-level low as the cyclone approaches southern New England, which induces a slight bend of Henri's forecast track to the left. Nearly all track models now show Henri's center reaching the coast of southern New England, and the new NHC track forecast has been nudged westward in the direction of HCCA and the other consensus aids. After day 3, Henri is forecast to eject northeastward across the Gulf of Maine toward Atlantic Canada. The strong shear affecting Henri is forecast to begin weakening later today, and SHIPS diagnostics indicate that it could drop to less than 10 kt in about 36 hours. In addition, Henri will be traversing very warm waters for the next 48 hours before it crosses the north wall of the Gulf Stream. Therefore, strengthening is anticipated for the next 2 days, with Henri likely to become a hurricane by Saturday. After 48 hours, Henri's expected slower motion over the colder water south of New England should induce quick weakening, but it may not be quick enough to keep Henri from reaching the coast as a hurricane. Faster weakening is anticipated after Henri's center moves over land, and simulated satellite imagery from the GFS and ECMWF models suggest that deep convection could dissipate by day 4, making Henri a post-tropical low at that time. Global models suggest that Henri may dissipate by day 5, but for the time being a day 5 point is being kept for continuity. Based on the new forecast, tropical-storm-force wind radii will be approaching the coast of southern New England in about 48 hours. Given the still-present uncertainties in Henri's future track and intensity and the hazards that the storm may cause, storm surge and hurricane watches are now being issued for portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts. Users are reminded to not focus on the exact forecast points as impacts will extend far from the center. Key Messages: 1. Henri is forecast to be near the northeast coast of the U.S. on Sunday and Monday, and the risks of storm surge, wind, and rain impacts in portions of southern New England and eastern Long Island are increasing. Hurricane and storm surge watches are now in effect for portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts. Additional watches or warnings may be required later today. 2. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. 3. Heavy rainfall may lead to flash, urban, and small stream flooding over portions of southern New England Sunday into Monday. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 30.2N 73.1W 55 KT 65 MPH 12H 20/1800Z 31.0N 73.5W 55 KT 65 MPH 24H 21/0600Z 33.0N 72.9W 60 KT 70 MPH 36H 21/1800Z 36.1N 71.8W 70 KT 80 MPH 48H 22/0600Z 39.1N 71.1W 75 KT 85 MPH 60H 22/1800Z 41.1N 71.3W 65 KT 75 MPH 72H 23/0600Z 42.2N 71.6W 50 KT 60 MPH...INLAND 96H 24/0600Z 43.5N 70.0W 35 KT 40 MPH...POST-TROPICAL 120H 25/0600Z 45.3N 63.0W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg Tropical Storm Henri Advisory Number 18 NWS National Hurricane Center Miami FL AL082021 500 AM EDT Fri Aug 20 2021 ...HENRI EXPECTED TO BECOME A HURRICANE BY SATURDAY... ...STORM SURGE AND HURRICANE WATCHES ISSUED FOR PORTIONS OF THE NORTHEASTERN UNITED STATES... SUMMARY OF 500 AM EDT...0900 UTC...INFORMATION ---------------------------------------------- LOCATION...30.2N 73.1W ABOUT 370 MI...600 KM SSE OF CAPE HATTERAS NORTH CAROLINA ABOUT 780 MI...1255 KM SSW OF NANTUCKET MASSACHUSETTS MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H PRESENT MOVEMENT...WNW OR 300 DEGREES AT 9 MPH...15 KM/H MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: A Storm Surge Watch has been issued for the south shore of Long Island from East Rockaway Inlet eastward to Montauk, the north shore of Long Island from Kings Point eastward to Montauk, and from Kings Point eastward to Sagamore Beach, Massachusetts, including Nantucket, Martha's Vineyard, and Block Island. A Hurricane Watch has been issued for Long Island from Fire Island Inlet eastward and from Port Jefferson Harbor eastward. A Hurricane Watch has also been issued from New Haven, Connecticut, eastward to Sagamore Beach, Massachusetts, including Nantucket, Martha's Vineyard, and Block Island. A Tropical Storm Watch has been issued west of Fire Island Inlet to East Rockaway Inlet, west of Port Jefferson Harbor, and west of New Haven. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Watch is in effect for... * South Shore of Long Island from East Rockaway Inlet to Montauk * North Shore of Long Island from Kings Point to Montauk * Kings Point New York to Sagamore Beach Massachusetts * Nantucket, Martha's Vineyard, and Block Island A Hurricane Watch is in effect for... * South Shore of Long Island from Fire Island Inlet to Montauk * North Shore of Long Island from Port Jefferson Harbor to Montauk * New Haven Connecticut to Sagamore Beach Massachusetts * Nantucket, Martha's Vineyard, and Block Island A Tropical Storm Watch is in effect for... * West of Fire Island Inlet to East Rockaway Inlet New York * West of Port Jefferson Harbor New York * West of New Haven Connecticut A Storm Surge Watch means there is a possibility of life- threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours. Interests elsewhere in the northeastern U.S. and Atlantic Canada should monitor the progress of Henri. Additional watches or warnings will likely be required later today. For storm information specific to your area, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. DISCUSSION AND OUTLOOK ---------------------- At 500 AM EDT (0900 UTC), the center of Tropical Storm Henri was located near latitude 30.2 North, longitude 73.1 West. Henri is moving toward the west-northwest near 9 mph (15 km/h). A turn toward the northwest is forecast later today, followed by a turn toward the north tonight. Henri is forecast to accelerate toward the north through early next week and approach the coast of southern New England on Sunday. Maximum sustained winds are near 65 mph (100 km/h) with higher gusts. Strengthening is forecast during the next few days, and Henri is expected to become a hurricane by Saturday. Tropical-storm-force winds extend outward up to 90 miles (150 km) from the center. The estimated minimum central pressure is 995 mb (29.39 inches). HAZARDS AFFECTING LAND ---------------------- STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide... Watch Hill, RI to Sagamore Beach, MA including Narragansett Bay, Buzzards Bay, Vineyard Sound, Nantucket Sound, and Cape Cod Bay....3-5 ft East Rockaway Inlet, NY to Montauk Point, NY...2-4 ft North shore of Long Island...2-4 ft Kings Point, NY to Watch Hill, RI...2-4 ft Cape May, NJ to East Rockaway Inlet, NY...1-3 ft The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and dangerous waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office. WIND: Hurricane conditions are possible within the hurricane watch area on Sunday, with tropical storm conditions possible by early Sunday. Tropical storm conditions are possible within the tropical storm watch area on Sunday. RAINFALL: Henri may produce rainfall amounts of 2 to 5 inches over southern New England Sunday into Monday, with isolated maximum totals near 8 inches. Heavy rainfall from Henri may result in areas of flash, urban, and small stream flooding. SURF: Swells generated by Henri should continue to affect Bermuda during the next day or so. Swells are expected to increase across much of the east coast of the U.S. and Atlantic Canada today and into the weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 800 AM EDT. Next complete advisory at 1100 AM EDT. $$ Forecaster Berg |