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Remnants of Fred Forecast Discussion Number 20

2021-08-14 16:51:04| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sat Aug 14 2021 000 WTNT41 KNHC 141450 TCDAT1 Remnants Of Fred Discussion Number 20 NWS National Hurricane Center Miami FL AL062021 1100 AM EDT Sat Aug 14 2021 A combination of shear caused by an upper-level trough over the Gulf of Mexico and land interaction has caused Fred to degenerate into an open wave. Surface observations from Cuba do not show a closed circulation, and satellite imagery shows at least two vorticity centers embedded in a large trough. The strongest convection is currently near and southeast of a vorticity center near the Isle of Youth. The initial position is a mean position between the vorticity center, and the initial intensity of 30 kt is based on Air Force Reserve Hurricane Hunter aircraft data to the northeast of the estimated center position. The global models forecast the upper-level trough to move northward and weaken during the next 24 h and indicate that Fred will re-form a closed circulation over the eastern Gulf of Mexico Sunday morning. Given the strength of the upper-level trough, that forecast may well be too bullish. However, given the agreement in the guidance, the revised intensity forecast will call for Fred to regain tropical cyclone status at about the 24 h point, followed by gradual strengthening in a less than ideal upper-level wind environment until landfall along the northern Gulf coast. After landfall, the system should weaken and dissipate between 96-120 h. The initial motion is a very uncertain 300/10. The system is expected to move west-northwestward to northwestward around the western periphery of the subtropical ridge, with a turn toward the north as the system nears the northern Gulf coast in 60-72 h. While the forecast guidance is in good agreement on this general scenario, there is uncertainty as to where the center of Fred will be when it re-forms. Therefore, users should not concentrate on the details of the forecast track, which could change quite a bit during the next 24-36 h. Although all coastal watches and warnings are discontinued at this time, the National Hurricane Center will continue 6-hourly advisories on the remnants of Fred in anticipation of re-development and the potential need for watches and warnings on the northern Gulf coast later in the weekend. KEY MESSAGES: 1. Today through Monday, heavy rainfall could lead to areal, urban, and small stream flooding impacts, and cause new and renewed river flooding, across southern Florida, the Big Bend, and Panhandle. From Monday onward, heavy rain and flood impacts could extend into other portions of the Southeast and into the southern and central Appalachians and Piedmont as Fred interacts with a front in the area. 2. Fred is forecast to regenerate as a tropical cyclone over the Gulf of Mexico on Sunday, and bring a risk of tropical storm conditions to portions of the northern Gulf coast, especially from coastal Mississippi to the Florida Panhandle beginning on Monday. Watches may be required for a portion of this area later in the weekend. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 23.3N 83.2W 30 KT 35 MPH...DISTURBANCE 12H 15/0000Z 24.1N 84.2W 30 KT 35 MPH...DISTURBANCE 24H 15/1200Z 25.7N 85.5W 30 KT 35 MPH...TROPICAL CYCLONE 36H 16/0000Z 27.4N 86.7W 35 KT 40 MPH 48H 16/1200Z 28.7N 87.4W 45 KT 50 MPH 60H 17/0000Z 30.0N 87.7W 45 KT 50 MPH 72H 17/1200Z 31.5N 87.5W 35 KT 40 MPH...INLAND 96H 18/1200Z 35.0N 86.5W 20 KT 25 MPH...POST-TROP/INLAND 120H 19/1200Z...DISSIPATED $$ Forecaster Beven

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Hurricane Linda Forecast Discussion Number 18

2021-08-14 16:35:04| Tropical Depression LIDIA

Issued at 800 AM PDT Sat Aug 14 2021

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Hurricane Linda Forecast Discussion Number 17

2021-08-14 10:50:05| Tropical Depression LIDIA

Issued at 300 AM MDT Sat Aug 14 2021

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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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