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Tropical Depression Eighteen Forecast Discussion Number 2
2021-09-23 04:38:42| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 22 2021 000 WTNT43 KNHC 230238 TCDAT3 Tropical Depression Eighteen Discussion Number 2 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Wed Sep 22 2021 The depression's organization has not improved since earlier this afternoon. An analysis of the ambiguities from 0000 UTC ASCAT-B data suggests that the surface circulation is just barely closed, with the center still attached to the northern end of a trough. Peak wind retrievals from the scatterometer pass were 25-30 kt, so the initial intensity remains 30 kt. Based on the ASCAT data, the depression appears to be moving just north of due west, or 275/13 kt. Low- to mid-level ridging to the north is expected to maintain the cyclone on a westward heading for the next 36 hours, followed by a path toward the west-northwest from day 2 through day 5. The more notable part of the forecast is the forward speed. Global models are showing anomalously strong 500-mb ridging developing over the eastern and central Caribbean Sea in 2 to 3 days, which is likely to block the depression's forward progress toward the end of the forecast period. In fact, the current NHC forecast has the system moving west-northwestward at only 7 or 8 kt well east of the Lesser Antilles on days 3 through 5. All this means that it will probably be a few more days before we have a better idea if and how the system might potentially threaten areas farther west. For the 5-day forecast period, there is a normal amount of spread among the track guidance, and the updated NHC forecast is very close to a blend of the TVCA and HCCA consensus aids. This solution is not too different from the previous forecast. Overall, an environment of low shear, warm sea surface temperatures, and a moist, unstable atmosphere appears conducive for strengthening. However, there is some sort of signal being conveyed by the global models (e.g., the GFS, ECMWF, and UKMET) whereby the cyclone's surface circulation does not really tighten up for another 24 to 48 hours. Given the system's current structure, this scenario seems plausible. Therefore, the updated NHC intensity forecast shows a slower rate of strengthening during the first 48 hours, just a bit below the intensity consensus in deference to the global model solutions. After 48 hours, the official forecast converges on top of the previous NHC forecast and still brings the cyclone to hurricane, and then possibly major hurricane, strength by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 10.2N 35.0W 30 KT 35 MPH 12H 23/1200Z 10.4N 37.0W 30 KT 35 MPH 24H 24/0000Z 10.9N 39.6W 35 KT 40 MPH 36H 24/1200Z 11.4N 42.1W 45 KT 50 MPH 48H 25/0000Z 12.0N 44.3W 55 KT 65 MPH 60H 25/1200Z 12.6N 46.0W 70 KT 80 MPH 72H 26/0000Z 13.2N 47.5W 80 KT 90 MPH 96H 27/0000Z 14.5N 50.2W 90 KT 105 MPH 120H 28/0000Z 16.0N 53.3W 100 KT 115 MPH $$ Forecaster Berg
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Tropical Depression Eighteen Wind Speed Probabilities Number 2
2021-09-23 04:38:13| National Hurricane Center (Atlantic)
Issued at 0300 UTC THU SEP 23 2021 000 FONT13 KNHC 230238 PWSAT3 TROPICAL DEPRESSION EIGHTEEN WIND SPEED PROBABILITIES NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC THU SEP 23 2021 AT 0300Z THE CENTER OF TROPICAL DEPRESSION EIGHTEEN WAS LOCATED NEAR LATITUDE 10.2 NORTH...LONGITUDE 35.0 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 30 KTS...35 MPH...55 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 00Z THU 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 00Z THU 12Z THU 00Z FRI 12Z FRI 00Z SAT 00Z SUN 00Z MON PERIODS TO TO TO TO TO TO TO 12Z THU 00Z FRI 12Z FRI 00Z SAT 00Z SUN 00Z MON 00Z TUE FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT $$ FORECASTER BERG
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Summary for Tropical Depression Eighteen (AT3/AL182021)
2021-09-23 04:37:43| National Hurricane Center (Atlantic)
...TROPICAL DEPRESSION EXPECTED TO TAKE ITS TIME CROSSING THE TROPICAL ATLANTIC... ...LOTS OF TIME TO MONITOR... As of 11:00 PM AST Wed Sep 22 the center of Eighteen was located near 10.2, -35.0 with movement W at 15 mph. The minimum central pressure was 1008 mb with maximum sustained winds of about 35 mph.
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Tropical Depression Eighteen Public Advisory Number 2
2021-09-23 04:37:43| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 22 2021 000 WTNT33 KNHC 230237 TCPAT3 BULLETIN Tropical Depression Eighteen Advisory Number 2 NWS National Hurricane Center Miami FL AL182021 1100 PM AST Wed Sep 22 2021 ...TROPICAL DEPRESSION EXPECTED TO TAKE ITS TIME CROSSING THE TROPICAL ATLANTIC... ...LOTS OF TIME TO MONITOR... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...10.2N 35.0W ABOUT 1955 MI...3150 KM ESE OF THE NORTHERN LEEWARD ISLANDS MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H PRESENT MOVEMENT...W OR 275 DEGREES AT 15 MPH...24 KM/H MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. DISCUSSION AND OUTLOOK ---------------------- At 1100 PM AST (0300 UTC), the center of Tropical Depression Eighteen was located near latitude 10.2 North, longitude 35.0 West. The depression is moving toward the west near 15 mph (24 km/h), and this general motion is expected to continue through early Friday. A slower motion toward the west-northwest is expected later on Friday and continuing into the weekend. Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Strengthening is forecast during the next few days, and the depression could become a tropical storm on Thursday. It is then forecast to become a hurricane over the weekend. The estimated minimum central pressure is 1008 mb (29.77 inches). HAZARDS AFFECTING LAND ---------------------- None. NEXT ADVISORY ------------- Next complete advisory at 500 AM AST. $$ Forecaster Berg
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Tropical Depression Eighteen Forecast Advisory Number 2
2021-09-23 04:37:43| National Hurricane Center (Atlantic)
Issued at 0300 UTC THU SEP 23 2021 000 WTNT23 KNHC 230237 TCMAT3 TROPICAL DEPRESSION EIGHTEEN FORECAST/ADVISORY NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182021 0300 UTC THU SEP 23 2021 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL DEPRESSION CENTER LOCATED NEAR 10.2N 35.0W AT 23/0300Z POSITION ACCURATE WITHIN 40 NM PRESENT MOVEMENT TOWARD THE WEST OR 275 DEGREES AT 13 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1008 MB MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 10.2N 35.0W AT 23/0300Z AT 23/0000Z CENTER WAS LOCATED NEAR 10.2N 34.4W FORECAST VALID 23/1200Z 10.4N 37.0W MAX WIND 30 KT...GUSTS 40 KT. FORECAST VALID 24/0000Z 10.9N 39.6W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 50NE 0SE 0SW 40NW. FORECAST VALID 24/1200Z 11.4N 42.1W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 60NE 40SE 0SW 40NW. FORECAST VALID 25/0000Z 12.0N 44.3W MAX WIND 55 KT...GUSTS 65 KT. 50 KT... 20NE 20SE 0SW 20NW. 34 KT... 70NE 50SE 20SW 40NW. FORECAST VALID 25/1200Z 12.6N 46.0W MAX WIND 70 KT...GUSTS 85 KT. 50 KT... 30NE 20SE 10SW 20NW. 34 KT... 80NE 60SE 30SW 50NW. FORECAST VALID 26/0000Z 13.2N 47.5W MAX WIND 80 KT...GUSTS 100 KT. 50 KT... 40NE 30SE 20SW 30NW. 34 KT... 90NE 70SE 40SW 60NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 27/0000Z 14.5N 50.2W MAX WIND 90 KT...GUSTS 110 KT. OUTLOOK VALID 28/0000Z 16.0N 53.3W MAX WIND 100 KT...GUSTS 120 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 10.2N 35.0W NEXT ADVISORY AT 23/0900Z $$ FORECASTER BERG
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