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Tropical Depression Grace Forecast Discussion Number 12

2021-08-16 10:48:10| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Aug 16 2021 930 WTNT42 KNHC 160848 TCDAT2 Tropical Depression Grace Discussion Number 12 NWS National Hurricane Center Miami FL AL072021 500 AM EDT Mon Aug 16 2021 The structure and organization of Tropical Depression Grace has changed little over the past several hours. An earlier ASCAT-B overpass showed that the circulation is elongated from the NE-SW, with peak winds of 30 kt. An Air Force Reserve Hurricane Hunter Aircraft investigated Grace a few hours ago, and indicated that the cyclone refuses to make the decrease in forward speed and turn to the west-northwest that most of the guidance has been calling for. The aircraft also measured peak flight level winds of 37 kt at 925 mb, which equates to about 28 kt at the surface. Although there were some SFMR vectors of tropical storm force, those winds were sampled in heavy rainfall and were likely not representative of the actual surface winds. Based on this data, the initial intensity is kept at 30 kt for this advisory. Grace is moving toward the west, or 275/13 kt. The forecast models continue to make a shift to the south, as they are coming into very good agreement on maintaining a strong mid-level ridge to the north of the cyclone throughout the forecast period. The latest track forecast was adjusted a little south of the previous one through the first couple of days of the forecast, with a larger shift to the south farther out in time. This forecast track remains to the north of the track consensus, so if the track models remain consistent, additional adjustments to the south will likely be made in the next forecast cycle. The evolution of the forecast track of Grace is having major implications on the future intensity of the cyclone. It is becoming more likely that the system will track over only the southern portion of Hispaniola, which would result in a lesser disruption of Grace's circulation. Furthermore, the more southern track would bring the cyclone over the warm waters of the northwestern Caribbean beginning on Tuesday. The environment over that portion of the Caribbean is not all that hostile, with about 10-15 kt of northerly shear being the main inhibiting factor for intensification. By midweek, Grace may interact with the Yucatan Peninsula, which should limit strengthening or perhaps weaken the system depending on the track. Once over the western Gulf of Mexico, late in the forecast period, some additional strengthening is expected, although the wind shear is forecast to increase slightly during that time frame. The latest NHC intensity forecast was raised slightly to reflect the additional time expected over water. However, this forecast is a little lower than most of the guidance. Key Messages: 1. Heavy rainfall across the Dominican Republic, Haiti, Cuba, Jamaica, and the Cayman Islands may lead to flash, urban, and small stream flooding, with the potential for mudslides highest in Haiti and the Dominican Republic. 2. Tropical storm conditions are possible over portions of Hispaniola today and tonight. 3. There is a risk of some wind and rainfall impacts across southeastern Cuba and Jamaica beginning Tuesday morning, and the Cayman Islands by Tuesday night. Interests there areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 17.4N 70.2W 30 KT 35 MPH 12H 16/1800Z 17.9N 72.2W 30 KT 35 MPH 24H 17/0600Z 18.6N 74.8W 30 KT 35 MPH 36H 17/1800Z 19.3N 77.4W 35 KT 40 MPH 48H 18/0600Z 20.1N 80.2W 35 KT 40 MPH 60H 18/1800Z 20.8N 83.3W 40 KT 45 MPH 72H 19/0600Z 21.6N 86.3W 45 KT 50 MPH 96H 20/0600Z 22.6N 91.8W 45 KT 50 MPH 120H 21/0600Z 23.4N 96.2W 50 KT 60 MPH $$ Forecaster Latto

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Hurricane Linda Forecast Discussion Number 25

2021-08-16 10:39:12| Tropical Depression LIDIA

Issued at 1100 PM HST Sun Aug 15 2021

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Tropical Depression Eight Forecast Discussion Number 1

2021-08-16 05:01:31| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Aug 15 2021 643 WTNT43 KNHC 160301 TCDAT3 Tropical Depression Eight Discussion Number 1 NWS National Hurricane Center Miami FL AL082021 1100 PM AST Sun Aug 15 2021 A small well-defined low pressure system located just east-northeast of Bermuda has produced persistent deep convection since this morning. Radar imagery from Bermuda along with geostationary and polar orbiting microwave satellite data show that the convection is sufficiently well organized to meet the definition for a tropical cyclone. Therefore advisories have been started on Tropical Depression Eight. The initial intensity is set at 25 kt, based on believable winds near that value in a pair of recent ASCAT overpasses. Dvorak estimates from TAFB and SAB were a little higher, so this estimate could be slightly conservative. Confidence in the forecast is reasonably high for the next 48 to 72 h. The depression should make a slow clockwise turn around Bermuda, steered by a mid-level ridge currently centered off the coast of the Carolinas. Warm SSTs should provide ample fuel to support at least slight strengthening during this period, despite expected northerly shear, and this is shown by all of the intensity guidance. The NHC forecast is very near the multi-model consensus for both track and intensity through that period. Beyond 72 h, the track and intensity models diverge quickly. The HWRF and COAMPS-TC models rapidly intensify the system to major hurricane strength. A stronger, deeper vortex would likely be steered generally westward through the end of the forecast period, influenced by a deeper-layer steering flow. However, the global models have a much weaker, shallower system which turns northward, and then possibly accelerates northeastward by day 5. As a result, the spread in the track guidance is nearly 800 n mi by day 5, with the GFS and HWRF taking the extreme positions to the northeast and southwest, respectively. The official track forecast takes a middle approach, and is between the various consensus aids at days 4 and 5. The NHC intensity forecast is slightly more conservative, and is below the consensus at the end of the period. Significant changes to the forecast may be required in subsequent advisory packages. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 33.2N 62.7W 25 KT 30 MPH 12H 16/1200Z 32.4N 62.8W 30 KT 35 MPH 24H 17/0000Z 31.5N 63.3W 35 KT 40 MPH 36H 17/1200Z 31.1N 64.0W 40 KT 45 MPH 48H 18/0000Z 31.0N 64.9W 45 KT 50 MPH 60H 18/1200Z 31.0N 66.1W 50 KT 60 MPH 72H 19/0000Z 31.2N 67.4W 55 KT 65 MPH 96H 20/0000Z 32.0N 68.5W 55 KT 65 MPH 120H 21/0000Z 33.5N 68.0W 55 KT 65 MPH $$ Forecaster Zelinsky

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Tropical Storm Fred Forecast Discussion Number 26

2021-08-16 04:44:37| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sun Aug 15 2021 000 WTNT41 KNHC 160244 TCDAT1 Tropical Storm Fred Discussion Number 26 NWS National Hurricane Center Miami FL AL062021 1000 PM CDT Sun Aug 15 2021 Fred remains a sheared tropical cyclone however the overall organization of the system has improved somewhat since this afternoon. The low-level center is embedded near the western edge of the primary convective mass, and there has been an overall increase in deep convection near and to the east of the center. An Air Force Reserve reconnaissance aircraft that has been investigating Fred this evening has reported that the pressure has fallen to 999 mb and it has found winds to support an initial intensity of 45 kt. The plane found a very small area of slightly stronger flight-level and SFMR winds well east of the center, but those winds appear to have been associated with a strong convective cell and are likely not representative of the system's overall intensity. Fred is moving north-northwestward or 330/08 kt, and this motion should continue overnight. The dynamical model guidance indicates that the tropical cyclone will turn northward on Monday as it approaches the coast of the Florida panhandle. A north- northeastward motion around the western periphery of a subtropical ridge over the western Atlantic should commence by the time the system makes landfall, and this general heading should continue until the system dissipates in a couple of days. The dynamical models envelope did not change much and the latest consensus aids were essentially along the previous NHC track. As a result, little alteration was made to the previous official track forecast. The cyclone is located within an area of moderate southwesterly vertical wind shear. However, most of the intensity guidance continues to suggest that Fred will strengthen a little over the next 12-18 hours. As the system nears the northern Gulf coast, the SHIPS guidance forecasts some increase in shear and the intensity models reflect this by showing a leveling off of Fred's intensity at that time. After landfall, Fred should weaken quickly and dissipate over the Tennessee Valley in a little more than 48 hours. The updated NHC intensity forecast is in good agreement within the HCCA and IVCN consensus aids. Users are reminded not to focus on the exact forecast track of Fred, since rainfall, storm surge, and wind hazards will extend over an area well east of the center. KEY MESSAGES: 1. Through Tuesday, heavy rainfall may lead to flash, urban, small stream, and isolated river flooding impacts across the Southeast, including portions of southern Florida, the Big Bend and Panhandle of Florida, southeast Alabama, portions of Georgia, and the western Carolinas. By the middle of the week as Fred lifts north and inland toward the Tennessee Valley, heavy rainfall and flooding may impact the southern and central Appalachians, and the Piedmont of the Southeast and Mid-Atlantic. 2. Dangerous storm surge inundation is possible along portions of the coast of the Florida Panhandle and the Florida Big Bend region, and a Storm Surge Warning is in effect for this area. Interests in these areas should follow any advice given by local officials. 3. Tropical storm conditions are expected in the Tropical Storm Warning area in the Florida Panhandle beginning on Monday. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 27.3N 85.9W 45 KT 50 MPH 12H 16/1200Z 28.6N 86.2W 50 KT 60 MPH 24H 17/0000Z 30.2N 86.1W 50 KT 60 MPH 36H 17/1200Z 32.3N 85.7W 30 KT 35 MPH...INLAND 48H 18/0000Z 34.4N 84.9W 20 KT 25 MPH...POST-TROP/INLAND 60H 18/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Grace Forecast Discussion Number 11

2021-08-16 04:41:37| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Aug 15 2021 000 WTNT42 KNHC 160241 TCDAT2 Tropical Depression Grace Discussion Number 11 NWS National Hurricane Center Miami FL AL072021 1100 PM AST Sun Aug 15 2021 An Air Force Reserve Hurricane Hunter Aircraft investigated Grace earlier this evening and found maximum flight level winds just less than 40 kt at 925 mb, which supports Grace's estimated 30 kt intensity. The plane also found that the depression still has a slightly elongated but closed surface circulation. During the past few hours, satellite imagery has shown a slight increase in convective banding features and associated heavy rain associated with Grace. That activity highlights the primary threat from Grace during the next 24 hours: prolonged heavy rainfall that could lead to flash and urban flooding along with the potential for mudslides over Puerto Rico and Hispaniola. The forecast for Grace is incredibly challenging. Imminent interactions with the high terrain of Hispaniola and Cuba could cause Grace to dissipate as soon as Monday evening. However, a track south of Cuba, as shown by recent runs of the GFS and COAMPS-TC, may allow Grace to maintain its tropical cyclone status and possibly even intensify. The HWRF even shows it becoming a hurricane over the western Caribbean, with the caveat that the model has produced several poor forecasts for Grace thus far. Although it is not explicitly forecast, slight intensification is still possible tonight or tomorrow morning before the center of Grace moves inland. After that time, the NHC forecast assumes Grace will continue as a tropical depression through 72 h. Once/if Grace makes it to the western Caribbean Sea and Gulf of Mexico in 3-4 days, it could have an opportunity to reorganize and intensify, and this is again shown in the official intensity forecast. That said, users are encouraged to not focus on the exact track or intensity forecasts at days 4 and 5. The track guidance has shifted south for this advisory, and generally calls for Grace to move westward to west-northwestward through the forecast period. The official track forecast has been shifted a little south once again, but is north of the most recent multi-model consensus. Key Messages: 1. Heavy rainfall across Puerto Rico, the Dominican Republic, and Haiti may lead to flash, urban, and small stream flooding, along with the potential for mudslides. 2. Tropical storm conditions are possible over portions of Hispaniola Monday and Monday night. 3. There is a risk of some wind and rainfall impacts across Cuba beginning Tuesday morning, but forecast uncertainty is much higher than usual. Interests there areas should monitor the progress of Grace and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 17.3N 68.6W 30 KT 35 MPH 12H 16/1200Z 17.7N 70.3W 30 KT 35 MPH 24H 17/0000Z 18.7N 72.8W 30 KT 35 MPH 36H 17/1200Z 19.5N 75.3W 30 KT 35 MPH 48H 18/0000Z 20.4N 78.1W 30 KT 35 MPH 60H 18/1200Z 21.2N 81.0W 30 KT 35 MPH 72H 19/0000Z 22.2N 84.0W 30 KT 35 MPH...INLAND 96H 20/0000Z 23.5N 89.0W 35 KT 40 MPH...OVER WATER 120H 21/0000Z 24.5N 93.5W 45 KT 50 MPH $$ Forecaster Zelinsky

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