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Tropical Storm Isaac Graphics

2018-09-11 19:40:58| National Hurricane Center (Atlantic)

5-Day Uncertainty Track last updated Tue, 11 Sep 2018 17:40:58 GMT Wind Speed Probabilities last updated Tue, 11 Sep 2018 15:34:32 GMT

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Summary for Tropical Storm Isaac (AT4/AL092018)

2018-09-11 19:40:34| National Hurricane Center (Atlantic)

...ISAAC CONTINUES MOVING WESTWARD... As of 2:00 PM AST Tue Sep 11 the center of Isaac was located near 14.6, -50.4 with movement W at 16 mph. The minimum central pressure was 996 mb with maximum sustained winds of about 70 mph.

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Tropical Storm Isaac Public Advisory Number 16A

2018-09-11 19:40:34| National Hurricane Center (Atlantic)

Issued at 200 PM AST Tue Sep 11 2018 326 WTNT34 KNHC 111740 TCPAT4 BULLETIN Tropical Storm Isaac Intermediate Advisory Number 16A NWS National Hurricane Center Miami FL AL092018 200 PM AST Tue Sep 11 2018 ...ISAAC CONTINUES MOVING WESTWARD... SUMMARY OF 200 PM AST...1800 UTC...INFORMATION ---------------------------------------------- LOCATION...14.6N 50.4W ABOUT 725 MI...1165 KM E OF THE LESSER ANTILLES MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H PRESENT MOVEMENT...W OR 270 DEGREES AT 16 MPH...26 KM/H MINIMUM CENTRAL PRESSURE...996 MB...29.42 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The meteorological service of Antigua and Barbuda has issued a Tropical Storm Watch for St. Kitts and Nevis. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Hurricane Watch is in effect for... * Guadeloupe * Martinique * Dominica A Tropical Storm Watch is in effect for... * Antigua * Montserrat * St. Kitts and Nevis 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 Leeward Islands should monitor the progress of Isaac as additional watches could be issued this afternoon or evening. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 200 PM AST (1800 UTC), the center of Tropical Storm Isaac was located with high-resolution GOES-16 visible satellite data near latitude 14.6 North, longitude 50.4 West. Isaac is moving toward the west near 16 mph (26 km/h), and this motion is expected to continue for the next few days. On the forecast track Isaac is anticipated to move near or over the central Lesser Antilles on Thursday and move into the eastern Caribbean Sea Thursday night. Maximum sustained winds remain near 70 mph (110 km/h) with higher gusts. Isaac is expected to be near hurricane strength when it moves through the central Lesser Antilles, with some weakening forecast afterward on Friday. Tropical-storm-force winds extend outward up to 105 miles (165 km) from the center. The estimated minimum central pressure is 996 mb (29.42 inches). HAZARDS AFFECTING LAND ---------------------- RAINFALL: Isaac is expected to produce total rainfall accumulations of 3 to 5 inches with isolated amounts near 10 inches across the southern Leeward Islands late this week, with 1 to 2 inches anticipated across portions of the Windward Islands. STORM SURGE: A storm surge of 2 to 4 feet above normal tide levels is possible near and to the north of where the center moves through the Lesser Antilles. Near the coast, the surge will be accompanied by large and destructive waves. WIND: Hurricane conditions are possible within the hurricane watch area by Thursday morning, with tropical storm conditions possible early Thursday in both the hurricane and tropical storm watch areas. SURF: Swells generated by Isaac will begin to affect portions of the Lesser Antilles on Wednesday afternoon. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next complete advisory at 500 PM AST. $$ Forecaster Blake

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Tropical Storm Isaac Forecast Discussion Number 16

2018-09-11 16:58:31| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 11 2018 079 WTNT44 KNHC 111458 TCDAT4 Tropical Storm Isaac Discussion Number 16 NWS National Hurricane Center Miami FL AL092018 1100 AM AST Tue Sep 11 2018 One-minute visible satellite data from GOES-16 indicate that the center of Isaac remains on the westward edge of the central dense overcast. The initial wind speed is kept at 60 kt, which is a compromise between the lower subjective estimates and higher ADTs and microwave estimates. This is a more uncertain estimate than normal due to the spread of the intensity fixes. The initial wind and 12 ft seas radii have been expanded out to the north based on TAFB estimates and microwave data. The intensity forecast continues to be tricky. Westerly shear should increase over the next couple of days, which would normally cause some weakening. However this effect could be tempered by increasing SSTs, mid-level moisture and instability in the path of the storm. Given our limited skill in forecasting intensity changes in marginal environments, plus the 5 or 10 kt of initial wind speed uncertainty, the official forecast will show no significant change in intensity for the next couple of days. Because of these uncertainties, a Hurricane Watch has been issued for many of the Leeward Islands, even though Isaac is not explicitly forecast to be a hurricane. Some weakening is indicated at long range after considering the global model trends in intensity, which have done fairly well for Isaac. The latest initial motion estimate is 270/14. Isaac is forecast to move westward at about the same speed for the next few days due to a mid-level ridge over the central Atlantic Ocean. Other than the UKMET model, there is not much spread in the guidance, except with the forward speed. Given the strength of the ridge, the cyclone isn't likely to slow down much, so the official forecast is basically along the previous forecast track but faster. The uncertainty increases at long range, and is somewhat dependent on the intensity of Isaac, but faster seems to be way to go given the weakening trend anticipated at that time. Key Messages: 1. Isaac is expected to be at or near hurricane intensity when it approaches the Lesser Antilles on Thursday, and hurricane and tropical storm watches have been issued for several islands. Interests in those areas should follow any advice given by their local officials. 2. Interests elsewhere in the Lesser Antilles should continue to monitor Isaac during the next couple of days, as additional watches could be needed for other islands. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 14.6N 49.7W 60 KT 70 MPH 12H 12/0000Z 14.6N 51.8W 60 KT 70 MPH 24H 12/1200Z 14.7N 54.4W 65 KT 75 MPH 36H 13/0000Z 14.9N 57.1W 60 KT 70 MPH 48H 13/1200Z 15.1N 59.9W 60 KT 70 MPH 72H 14/1200Z 15.5N 65.5W 55 KT 65 MPH 96H 15/1200Z 15.5N 71.0W 50 KT 60 MPH 120H 16/1200Z 15.5N 75.0W 50 KT 60 MPH $$ Forecaster Blake

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