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Hurricane Linda Forecast Advisory Number 17

2021-08-14 10:45:32| Tropical Depression LIDIA

Issued at 0900 UTC SAT AUG 14 2021

Tropical Storm Grace Forecast Discussion Number 4

2021-08-14 10:40:14| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Aug 14 2021 000 WTNT42 KNHC 140840 TCDAT2 Tropical Storm Grace Discussion Number 4 NWS National Hurricane Center Miami FL AL072021 500 AM AST Sat Aug 14 2021 The cyclone has become a little better organized overnight, with an area of concentrated convection persisting over the center for the past several hours. The system remains compact, with the convective canopy about 100 n mi in diameter, while earlier ASCAT data revealed winds greater than 25 kt extended only about 30 n mi from its center, with peak winds of 27 kt. Despite the weaker maximum winds sampled earlier this evening, the increase in organization of such a small system has likely produced a notable increase in the surface winds near the center. In addition the latest Dvorak intensity estimates from TAFB, SAB, and the UW-CIMSS ADT and SATCON suggest that the intensity is now somewhere between 30 and 45 kt. Based on a conservative blend of these values, it is estimated that the Tropical Depression Seven has strengthened into 35-kt Tropical Storm Grace. Grace continues to move quickly westward, with an initial motion of 280/19 kt. A strong mid-level ridge to the north of the storm should continue to steer it westward for the next few days. Beyond that time, the forecast models begin to diverge in their track solutions, as they vary in the strength of the ridge. Overall, the models have trended toward a stronger, more persistent ridge to the north of the cyclone for the latter half of the forecast period, and as such the model solutions are generally showing a track that lies a bit south of the previous runs for those time periods. The official NHC forecast track is little changed through 72 h and lies near the middle of the tightly clustered track guidance. Beyond 72 h, the forecast track has been shifted slightly to the south, but still lies to north of the consensus model tracks. The earlier bout of wind shear that had entrained surrounding dry air into Grace appears to have abated, at least in the short term. And, global models indicate that the shear will remain low for about the next 24-36 h while the cyclone moves over increasing SSTs. Therefore, it is reasonable to assume that strengthening should occur over the next day or so. Thereafter, the intensity forecast becomes somewhat complicated as the system is forecast to interact with an upper-level trough while possibly crossing the Greater Antilles at the same time. Slight weakening is indicated in the NHC intensity forecast as the system crosses the northern portion of the Dominican Republic early next week. Thereafter, moderate to strong northerly shear is forecast to impact Grace as the system moves into the flow on the western side of an upper-level trough over the western Atlantic. This shear should prevent any further strengthening through the end of the forecast period. The intensity forecast is a little lower than a blend of the NOAA HCCA and IVCN consensus, as there is likely a high bias from the HWRF in these solutions. The latter portion of the NHC intensity forecast is of lower-than-normal confidence due to the potential for a longer amount of time over the rugged terrain of the Greater Antilles than indicated, and also due to the fragile nature of the small cyclone and the possible effects of the stronger shear later in the forecast period. Key Messages: 1. Tropical storm conditions are expected in portions of the Leeward Islands by tonight or early Sunday, and the U.S. Virgin Islands and Puerto Rico on Sunday. Tropical storm conditions are also possible over the British Virgin Islands on Sunday. The risk of strong winds will then spread westward to the Dominican Republic Sunday night and Monday. 2. Heavy rainfall could lead to flash and urban flooding over the Leeward and Virgin Islands. Across Puerto Rico, heavy rainfall may lead to flash, urban and small stream flooding, along with the potential for mudslides. 3. There is a risk of wind and rainfall impacts across Haiti, the Turks and Caicos Islands, the southeastern Bahamas, Cuba, and Florida next week, and interests in those areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 15.8N 55.6W 35 KT 40 MPH 12H 14/1800Z 16.2N 58.5W 35 KT 40 MPH 24H 15/0600Z 16.9N 61.8W 40 KT 45 MPH 36H 15/1800Z 17.7N 64.8W 45 KT 50 MPH 48H 16/0600Z 18.3N 67.3W 45 KT 50 MPH 60H 16/1800Z 18.9N 69.4W 40 KT 45 MPH...INLAND 72H 17/0600Z 19.8N 71.5W 40 KT 45 MPH...INLAND 96H 18/0600Z 21.9N 75.6W 40 KT 45 MPH...OVER WATER 120H 19/0600Z 24.5N 79.7W 40 KT 45 MPH $$ Forecaster Latto

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Tropical Storm Grace Forecast Advisory Number 4

2021-08-14 10:39:05| National Hurricane Center (Atlantic)

Issued at 0900 UTC SAT AUG 14 2021 000 WTNT22 KNHC 140838 TCMAT2 TROPICAL STORM GRACE FORECAST/ADVISORY NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072021 0900 UTC SAT AUG 14 2021 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... A TROPICAL STORM WARNING HAS BEEN ISSUED FOR THE U.S. VIRGIN ISLANDS AND PUERTO RICO...INCLUDING VIEQUES AND CULEBRA. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A TROPICAL STORM WARNING IS IN EFFECT FOR... * ANTIGUA AND BARBUDA...ANGUILLA...ST. KITTS AND NEVIS...AND MONTSERRAT * SABA AND SINT EUSTATIUS * SINT MAARTEN * ST. MARTIN AND ST. BARTHELEMY * U.S. VIRGIN ISLANDS * PUERTO RICO...INCLUDING VIEQUES AND CULEBRA A TROPICAL STORM WATCH IS IN EFFECT FOR... * BRITISH VIRGIN ISLANDS A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS. A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS. INTERESTS IN THE DOMINICAN REPUBLIC SHOULD MONITOR THE PROGRESS OF THIS SYSTEM. ADDITIONAL WATCHES AND WARNINGS WILL LIKELY BE REQUIRED FOR THIS AREA LATER TODAY. TROPICAL STORM CENTER LOCATED NEAR 15.8N 55.6W AT 14/0900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 19 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1007 MB MAX SUSTAINED WINDS 35 KT WITH GUSTS TO 45 KT. 34 KT....... 20NE 0SE 0SW 20NW. 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 15.8N 55.6W AT 14/0900Z AT 14/0600Z CENTER WAS LOCATED NEAR 15.6N 54.7W FORECAST VALID 14/1800Z 16.2N 58.5W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 20NE 0SE 0SW 20NW. FORECAST VALID 15/0600Z 16.9N 61.8W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 30NE 0SE 0SW 30NW. FORECAST VALID 15/1800Z 17.7N 64.8W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 40NE 0SE 0SW 40NW. FORECAST VALID 16/0600Z 18.3N 67.3W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 40NE 0SE 0SW 40NW. FORECAST VALID 16/1800Z 18.9N 69.4W...INLAND MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 40NE 30SE 0SW 40NW. FORECAST VALID 17/0600Z 19.8N 71.5W...INLAND MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 40NE 30SE 0SW 40NW. 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 18/0600Z 21.9N 75.6W...OVER WATER MAX WIND 40 KT...GUSTS 50 KT. OUTLOOK VALID 19/0600Z 24.5N 79.7W MAX WIND 40 KT...GUSTS 50 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 15.8N 55.6W INTERMEDIATE PUBLIC ADVISORY...WTNT32 KNHC/MIATCPAT2...AT 14/1200Z NEXT ADVISORY AT 14/1500Z $$ FORECASTER LATTO

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Hurricane Linda Forecast Discussion Number 16

2021-08-14 05:03:25| Tropical Depression LIDIA

Issued at 900 PM MDT FRI AUG 13 2021

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Tropical Depression Seven Forecast Discussion Number 3

2021-08-14 04:59:57| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Aug 13 2021 000 WTNT42 KNHC 140259 TCDAT2 Tropical Depression Seven Discussion Number 3 NWS National Hurricane Center Miami FL AL072021 1100 PM AST Fri Aug 13 2021 While Tropical Depression Seven has maintained a irregularly shaped cirrus canopy of deep cold cloud tops near its estimated center, the convection does not appear well organized. Several SSMIS microwave passes between 2011 UTC and 2205 UTC did not reveal much organization under the cirrus, with just a few patches of deeper convection contributing to the larger stratiform region. A helpful ASCAT-B pass at 0030 UTC showed that the center was near the southeastern end of this cirrus canopy, and found peak winds lower than earlier today at only 27 kt. The 0000 UTC subjective Dvorak estimates were T2.5/35 kt from SAB and T2.5/30 kt from TAFB and the most recent objective ADT estimate was in between at T2.2/32 kt. A blend of these data support keeping the initial intensity at 30-kt for this advisory. The small cyclone continues to move quickly off to the west at 280/18 kt. A large low- to mid-level ridge draped across the central and western North Atlantic is expected to maintain the system on a general west-northwest heading, though with gradual deceleration as the ridge is eroded some by a mid- to upper-tropospheric trough. The latest track guidance remains tightly clustered but a bit more poleward through the first 72 hours. Afterwards, more track guidance spread becomes apparent. A quick look at the latest ECMWF ensemble guidance suggest that some of this spread is driven by the forecast intensity of the system, with stronger members taking the cyclone on a more poleward track. For now, the latest NHC track forecast is fairly close to, but a little poleward of the previous track. This track remains close to the HCCA and TVCN consensus aids, and roughly splits the difference between the deterministic GFS and ECMWF model solutions. The intensity forecast is somewhat conflicting. Even though both the GFS & ECMWF based SHIPS guidance depict low 200-850 hPa vertical wind shear between 5-10 knots over the next 48 hours, the depression is also embedded in very dry mid-level air, with 700-500 hPa layer mean relative humidity as low as 44 percent currently in the ECMWF-SHIPS. In addition, the system is moving rapidly westward, and a continued fast motion in the short-term may result in higher westerly mid-level shear which may have a larger than normal effect to a small tropical cyclone in a very dry environment. After 48 hours, vertical wind shear out of the northwest is expected to increase, ahead of a large upper-level trough digging southwestward, upstream of the cyclone. Moreover, land interaction with both Puerto Rico and Hispaniola remains a distinct possibility, especially if the cyclone tracks left of the current forecast track. It is worth noting the latest HWRF run continues to be a extreme outlier with a much higher intensity than the remaining guidance. In fact, much of global model guidance and COAMPS-TC regional hurricane model barely maintains a closed circulation over the next 36-48 hours. I have elected to maintain a very similar forecast to the previous advisory, with peak winds of only 45 kt in 48-60 hours. This forecast remains conservative and is still lower than the SHIPS and HCCA intensity guidance. Key Messages: 1. Tropical storm conditions are expected in portions of the Leeward Islands late Saturday or early Sunday, and are possible over the Virgin Islands and Puerto Rico on Sunday. The risk of strong winds will then spread westward to the Dominican Republic Sunday night and Monday. 2. Heavy rainfall could lead to flash and urban flooding over the Leeward and Virgin Islands. Across Puerto Rico, heavy rainfall may lead to flash, urban and small stream flooding, along with the potential for mudslides. 3. There is a risk of wind and rainfall impacts across Haiti, the Turks and Caicos Islands, the southeastern Bahamas, and Cuba next week, and interests in those areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 15.5N 53.8W 30 KT 35 MPH 12H 14/1200Z 16.0N 56.8W 35 KT 40 MPH 24H 15/0000Z 16.7N 60.3W 35 KT 40 MPH 36H 15/1200Z 17.5N 63.5W 40 KT 45 MPH 48H 16/0000Z 18.3N 66.2W 45 KT 50 MPH...INLAND 60H 16/1200Z 18.9N 68.2W 45 KT 50 MPH...OVER WATER 72H 17/0000Z 19.6N 70.4W 35 KT 40 MPH...INLAND 96H 18/0000Z 21.7N 74.3W 40 KT 45 MPH...OVER WATER 120H 19/0000Z 24.3N 78.6W 40 KT 45 MPH $$ Forecaster Papin/Brown

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