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Tropical Storm Isaac Forecast Discussion Number 17
2018-09-11 22:34:02| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Sep 11 2018 014 WTNT44 KNHC 112033 TCDAT4 Tropical Storm Isaac Discussion Number 17 NWS National Hurricane Center Miami FL AL092018 500 PM AST Tue Sep 11 2018 Microwave and visible satellite data show that the center of Isaac is partially exposed on the western edge of the central dense overcast. Perhaps Isaac is a little weaker than earlier, but a blend of the latest subjective and objective estimates still gives an uncertain initial wind speed of about 60 kt. We should have a better idea of the maximum winds by tomorrow morning when a NOAA Hurricane Hunter enters the storm, or if we get lucky with a scatterometer pass this evening. Isaac is barely holding on in the face of increasing shear, which is much more evident in the 300-500 mb layer than a conventional analysis at 200 mb. However, convection could redevelop near the center while the storm moves over warming SSTs into a more moist and unstable environment east of the Lesser Antilles. These conflicting factors lead to a forecast of little change in the winds of Isaac until the cyclone moves into the eastern Caribbean. I should mention that the short-term trend on satellite makes me think the intensity forecast is too high over the next 36 hours. Yet, given our limited skill in forecasting intensity changes in marginal environments, plus the 5 or 10 kt of initial wind speed uncertainty, this is the course of least regret. We can see if this trend becomes more consistent before making substantial changes on the next advisory. Model guidance is very divergent in the long range for Isaac, with the regional hurricane and statistical models showing intensification, while the global models show continued weakening. The global models have done fairly well with this cyclone, so the forecast will lean more heavily on their weaker solutions. The latest initial motion estimate is 270/15, a little faster than before. Isaac is forecast to move westward at roughly the same speed for the next few days due to a mid-level ridge over the central Atlantic Ocean. Model guidance is tightly clustered on this cycle, with the UKMET now coming into good agreement with the rest of the guidance. The only change to this forecast is to accelerate Isaac roughly 1 kt over the course of the prediction, which over the course of a 5-day forecast results in a sizable westward shift. This forecast could still be too slow, since the GFS and ECMWF are a bit ahead of the new NHC track prediction. 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, and warnings will likely be issued this evening. 2. Interests elsewhere in the Lesser Antilles should continue to monitor Isaac during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 14.6N 51.3W 60 KT 70 MPH 12H 12/0600Z 14.6N 53.4W 60 KT 70 MPH 24H 12/1800Z 14.8N 56.2W 60 KT 70 MPH 36H 13/0600Z 15.0N 59.2W 60 KT 70 MPH 48H 13/1800Z 15.3N 62.3W 55 KT 65 MPH 72H 14/1800Z 15.5N 68.5W 50 KT 60 MPH 96H 15/1800Z 15.5N 73.5W 45 KT 50 MPH 120H 16/1800Z 15.5N 77.5W 45 KT 50 MPH $$ Forecaster Blake
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Tropical Storm Isaac Wind Speed Probabilities Number 17
2018-09-11 22:33:32| National Hurricane Center (Atlantic)
Issued at 2100 UTC TUE SEP 11 2018 730 FONT14 KNHC 112033 PWSAT4 TROPICAL STORM ISAAC WIND SPEED PROBABILITIES NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092018 2100 UTC TUE SEP 11 2018 AT 2100Z THE CENTER OF TROPICAL STORM ISAAC WAS LOCATED NEAR LATITUDE 14.6 NORTH...LONGITUDE 51.3 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 60 KTS...70 MPH...110 KM/H. Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH) ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST ...34 KT (39 MPH... 63 KM/H)... ...50 KT (58 MPH... 93 KM/H)... ...64 KT (74 MPH...119 KM/H)... FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY) (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN 18Z TUE AND THE FORECAST HOUR (CUMULATIVE PROBABILITY) PROBABILITIES ARE GIVEN IN PERCENT X INDICATES PROBABILITIES LESS THAN 1 PERCENT PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT. PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY 64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT. - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM TIME 18Z TUE 06Z WED 18Z WED 06Z THU 18Z THU 18Z FRI 18Z SAT PERIODS TO TO TO TO TO TO TO 06Z WED 18Z WED 06Z THU 18Z THU 18Z FRI 18Z SAT 18Z SUN FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT PT GALLINAS 34 X X( X) X( X) X( X) 1( 1) 5( 6) 1( 7) CURACAO 34 X X( X) X( X) X( X) 3( 3) 1( 4) X( 4) MONTEGO BAY 34 X X( X) X( X) X( X) X( X) 2( 2) 6( 8) KINGSTON 34 X X( X) X( X) X( X) X( X) 1( 1) 5( 6) LES CAYES 34 X X( X) X( X) X( X) X( X) 3( 3) 1( 4) PORT-AU-PRINCE 34 X X( X) X( X) X( X) 1( 1) 8( 9) 1(10) CAPE BEATA 34 X X( X) X( X) X( X) 5( 5) 14(19) 1(20) CAPE BEATA 50 X X( X) X( X) X( X) X( X) 4( 4) X( 4) PUERTO PLATA 34 X X( X) X( X) X( X) 1( 1) 3( 4) X( 4) SANTO DOMINGO 34 X X( X) X( X) X( X) 3( 3) 3( 6) X( 6) PONCE PR 34 X X( X) X( X) X( X) 8( 8) X( 8) X( 8) AGUADILLA PR 34 X X( X) X( X) X( X) 5( 5) X( 5) X( 5) SAN JUAN PR 34 X X( X) X( X) 1( 1) 4( 5) X( 5) X( 5) VIEQUES PR 34 X X( X) X( X) 4( 4) 13(17) X(17) X(17) SAINT THOMAS 34 X X( X) X( X) 4( 4) 10(14) X(14) X(14) SAINT CROIX 34 X X( X) X( X) 7( 7) 16(23) X(23) X(23) SAINT CROIX 50 X X( X) X( X) X( X) 4( 4) X( 4) X( 4) SAINT MAARTEN 34 X X( X) 2( 2) 9(11) 7(18) X(18) X(18) ST KITTS-NEVIS 34 X X( X) 4( 4) 19(23) 7(30) X(30) X(30) ST KITTS-NEVIS 50 X X( X) X( X) 3( 3) 2( 5) X( 5) X( 5) ST KITTS-NEVIS 64 X X( X) X( X) 1( 1) 1( 2) X( 2) X( 2) BARBUDA 34 X X( X) 6( 6) 15(21) 3(24) X(24) X(24) BARBUDA 50 X X( X) X( X) 2( 2) 1( 3) X( 3) X( 3) ANTIGUA 34 X X( X) 7( 7) 24(31) 2(33) X(33) X(33) ANTIGUA 50 X X( X) X( X) 5( 5) 1( 6) X( 6) X( 6) ANTIGUA 64 X X( X) X( X) 2( 2) X( 2) X( 2) X( 2) GUADELOUPE 34 X X( X) 13(13) 40(53) 2(55) X(55) X(55) GUADELOUPE 50 X X( X) 1( 1) 13(14) 1(15) X(15) X(15) GUADELOUPE 64 X X( X) X( X) 3( 3) X( 3) X( 3) X( 3) AVES 34 X X( X) 3( 3) 27(30) 27(57) X(57) X(57) AVES 50 X X( X) X( X) 5( 5) 16(21) X(21) X(21) AVES 64 X X( X) X( X) 1( 1) 4( 5) X( 5) X( 5) DOMINICA 34 X X( X) 16(16) 45(61) 2(63) X(63) X(63) DOMINICA 50 X X( X) 1( 1) 24(25) 1(26) X(26) X(26) DOMINICA 64 X X( X) X( X) 6( 6) X( 6) X( 6) X( 6) MARTINIQUE 34 X 1( 1) 16(17) 33(50) 1(51) X(51) X(51) MARTINIQUE 50 X X( X) 2( 2) 17(19) 1(20) X(20) X(20) MARTINIQUE 64 X X( X) X( X) 5( 5) X( 5) X( 5) X( 5) SAINT LUCIA 34 X 1( 1) 7( 8) 14(22) 1(23) X(23) X(23) SAINT LUCIA 50 X X( X) 1( 1) 5( 6) X( 6) X( 6) X( 6) SAINT LUCIA 64 X X( X) X( X) 1( 1) 1( 2) X( 2) X( 2) SAINT VINCENT 34 X X( X) 4( 4) 5( 9) 1(10) X(10) X(10) BARBADOS 34 X 2( 2) 6( 8) 2(10) X(10) X(10) X(10) GRENADA 34 X X( X) 2( 2) 1( 3) 1( 4) X( 4) X( 4) TRINIDADTOBAGO 34 X X( X) 2( 2) 1( 3) X( 3) X( 3) X( 3) $$ FORECASTER BLAKE
Summary for Tropical Storm Isaac (AT4/AL092018)
2018-09-11 22:33:03| National Hurricane Center (Atlantic)
...WARNINGS LIKELY TO BE ISSUED TONIGHT FOR ISAAC... As of 5:00 PM AST Tue Sep 11 the center of Isaac was located near 14.6, -51.3 with movement W at 17 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 17
2018-09-11 22:33:03| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Sep 11 2018 563 WTNT34 KNHC 112032 TCPAT4 BULLETIN Tropical Storm Isaac Advisory Number 17 NWS National Hurricane Center Miami FL AL092018 500 PM AST Tue Sep 11 2018 ...WARNINGS LIKELY TO BE ISSUED TONIGHT FOR ISAAC... SUMMARY OF 500 PM AST...2100 UTC...INFORMATION ---------------------------------------------- LOCATION...14.6N 51.3W ABOUT 670 MI...1075 KM E OF THE LESSER ANTILLES MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H PRESENT MOVEMENT...W OR 270 DEGREES AT 17 MPH...28 KM/H MINIMUM CENTRAL PRESSURE...996 MB...29.42 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. 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 Tropical Storm Watch means that tropical storm conditions are possible within the watch area. Interests elsewhere in the Leeward Islands should monitor the progress of Isaac as additional watches or warnings will likely be issued tonight. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 500 PM AST (2100 UTC), the center of Tropical Storm Isaac was located near latitude 14.6 North, longitude 51.3 West. Isaac is moving toward the west near 17 mph (28 km/h), and this general 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, move into the eastern Caribbean Sea Thursday night, and move into the central Caribbean Sea by the weekend. 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 and Saturday. 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 Martinique, Dominica, and Guadeloupe, with 1 to 2 inches anticipated across the remaining Windward and Leeward 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 overnight Wednesday 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 intermediate advisory at 800 PM AST. Next complete advisory at 1100 PM AST. $$ Forecaster Blake
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Tropical Storm Isaac Forecast Advisory Number 17
2018-09-11 22:32:35| National Hurricane Center (Atlantic)
Issued at 2100 UTC TUE SEP 11 2018 612 WTNT24 KNHC 112032 TCMAT4 TROPICAL STORM ISAAC FORECAST/ADVISORY NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092018 2100 UTC TUE SEP 11 2018 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... NONE. 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 TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA. INTERESTS ELSEWHERE IN THE LEEWARD ISLANDS SHOULD MONITOR THE PROGRESS OF ISAAC AS ADDITIONAL WATCHES OR WARNINGS WILL LIKELY BE ISSUED TONIGHT. TROPICAL STORM CENTER LOCATED NEAR 14.6N 51.3W AT 11/2100Z POSITION ACCURATE WITHIN 20 NM PRESENT MOVEMENT TOWARD THE WEST OR 270 DEGREES AT 15 KT ESTIMATED MINIMUM CENTRAL PRESSURE 996 MB MAX SUSTAINED WINDS 60 KT WITH GUSTS TO 75 KT. 50 KT....... 20NE 0SE 0SW 20NW. 34 KT....... 90NE 20SE 20SW 90NW. 12 FT SEAS..180NE 60SE 60SW 180NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 14.6N 51.3W AT 11/2100Z AT 11/1800Z CENTER WAS LOCATED NEAR 14.6N 50.6W FORECAST VALID 12/0600Z 14.6N 53.4W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 20NE 0SE 0SW 20NW. 34 KT... 90NE 20SE 20SW 80NW. FORECAST VALID 12/1800Z 14.8N 56.2W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 30NE 10SE 10SW 20NW. 34 KT... 90NE 30SE 30SW 70NW. FORECAST VALID 13/0600Z 15.0N 59.2W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 30NE 10SE 10SW 20NW. 34 KT... 80NE 50SE 30SW 60NW. FORECAST VALID 13/1800Z 15.3N 62.3W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 30NE 20SE 10SW 20NW. 34 KT... 80NE 50SE 30SW 60NW. FORECAST VALID 14/1800Z 15.5N 68.5W MAX WIND 50 KT...GUSTS 60 KT. 50 KT... 30NE 0SE 0SW 20NW. 34 KT... 80NE 50SE 30SW 60NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 15/1800Z 15.5N 73.5W MAX WIND 45 KT...GUSTS 55 KT. OUTLOOK VALID 16/1800Z 15.5N 77.5W MAX WIND 45 KT...GUSTS 55 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 14.6N 51.3W NEXT ADVISORY AT 12/0300Z $$ FORECASTER BLAKE
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