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Tropical Storm Linda Forecast Discussion Number 9

2021-08-12 10:43:13| Tropical Depression LIDIA

Issued at 300 AM MDT Thu Aug 12 2021

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Tropical Depression Kevin Forecast Discussion Number 20

2021-08-12 10:38:15| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Aug 12 2021 000 WTPZ41 KNHC 120838 TCDEP1 Tropical Depression Kevin Discussion Number 20 NWS National Hurricane Center Miami FL EP112021 200 AM PDT Thu Aug 12 2021 Kevin is barely a tropical cyclone, as its exposed low-level center has been displaced over 100 n mi northeast of a few small bursts of convection for most of the night. In fact, the last semblance of organized convection with this sheared cyclone ended around 11/2100 UTC. If Kevin is unable to generate any organized convection soon, the system could be declared a post-tropical remnant low later this morning. Overnight ASCAT-A/B passes only showed 25 to 30-kt winds, primarily in the eastern semicircle of Kevin. Therefore, the initial intensity is lowered to 30 kt for this advisory, which makes Kevin a tropical depression. Based on recent scatterometer fixes, it appears the broad center of Kevin is moving slightly more west-northwestward than before, or 295/10 kt. A general west-northwest to northwest motion should continue through dissipation as the system moves along the southwestern side of a deep-layer ridge. The track guidance remains in good agreement, and the official NHC track forecast has been nudged slightly southward from the previous one based on the initial motion adjustment. The cyclone is already north of the 26 deg C isotherm, and it will move over progressively cooler waters and into a drier, more stable environment during the next couple of days. Thus, the development of new, organized convection near Kevin's center seems very unlikely. The official NHC forecast now shows Kevin degenerating to a remnant low later today, in agreement with the latest GFS and ECMWF model simulated satellite imagery. The remnant low should gradually spin down over the next couple of days before dissipating this weekend. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 22.3N 119.3W 30 KT 35 MPH 12H 12/1800Z 23.2N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 13/0600Z 24.4N 123.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 13/1800Z 25.8N 125.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 14/0600Z 27.4N 127.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 14/1800Z 29.0N 129.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 15/0600Z...DISSIPATED $$ Forecaster Reinhart/Cangialosi

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Tropical Depression Fred Forecast Discussion Number 11

2021-08-12 10:35:40| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Aug 12 2021 763 WTNT41 KNHC 120835 TCDAT1 Tropical Depression Fred Discussion Number 11 NWS National Hurricane Center Miami FL AL062021 500 AM EDT Thu Aug 12 2021 The rugged terrain of Hispaniola has taken a toll on Fred. Satellite images and surface observations indicate that the circulation is stretched out and seems to resemble a trough at the surface. The system is now emerging back over water and is located between Haiti, eastern Cuba, and the southeastern Bahamas. Most of the associated showers and thunderstorms are located to the east of the estimated center, with heavy rains continuing over portions of Hispaniola. The initial intensity is estimated to be 30 kt, but there is limited data to confirm this. Both the NOAA and Air Force Hurricane Hunters will be investigating Fred later this morning, and the data from both planes will be helpful in estimating Fred's strength and structure. Fred appears to be moving west-northwestward at about 14 kt. The track forecast reasoning has not changed much. A subtropical ridge currently situated to the north of Fred over the western Atlantic should continue to steer the system west-northwestward for the next 36 to 48 hours. This motion should take the storm just north of or across Cuba and the southeastern Bahamas during that time period. By the weekend, the models suggest that Fred will be rounding the western periphery of the ridge, which will likely a cause a slow down and a gradual turn to the northwest and then the north across portions of the Florida Keys, the Florida peninsula, and the eastern Gulf of Mexico. There is uncertainty in exactly where and when Fred will make that turn to the right, with models currently spanning a region from over Florida to the east-central Gulf of Mexico. The NHC track forecast remains on the right side of the guidance envelope, near the typically more skillful global models and consensus aids. Fred is currently in an environment of about 20 kt of westerly vertical wind shear. This shear is expected to persist during the next day or so, and those unfavorable winds combined with some land interaction with Cuba should prevent the system from strengthening much, if at all, during that time period. The shear could lessen on Friday and since SSTs are very warm and there is abundant environmental moisture, some strengthening seems likely when Fred is approaching the Florida Keys and south Florida Friday night and Saturday. After that time, the intensity forecast becomes more complicated by how much land interaction there will be with Florida. Since the official forecast shows a track over the eastern Gulf, additional strengthening is predicted before Fred makes its final landfall along the Florida Big Bend region or Florida panhandle late in the weekend or early next week. However, that part of the intensity forecast, since it will be very track dependent, is more uncertain. KEY MESSAGES: 1. Continued heavy rainfall today could lead to flash, urban, and small stream flooding, along with possible rapid river rises and potential mudslides in the Dominican Republic and Haiti. 2. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas this morning, and in portions of Cuba later today. 3. Beginning Friday, heavy rainfall could lead to areal, urban, and small stream flooding, and possible rapid river rises across southern Florida. Heavy rainfall associated with Fred will impact the remainder of Florida and parts of the Southeast this weekend and into next week. 4. There is a risk of tropical storm conditions beginning early Saturday in the Florida Keys and south Florida. These conditions are expected to spread northward along portions of the Florida west coast and the Florida Panhandle through Monday. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 20.2N 73.5W 30 KT 35 MPH 12H 12/1800Z 21.0N 75.1W 30 KT 35 MPH 24H 13/0600Z 22.0N 77.2W 30 KT 35 MPH 36H 13/1800Z 23.0N 79.1W 35 KT 40 MPH 48H 14/0600Z 23.8N 80.3W 35 KT 40 MPH 60H 14/1800Z 25.1N 81.4W 40 KT 45 MPH 72H 15/0600Z 26.6N 82.6W 45 KT 50 MPH 96H 16/0600Z 29.5N 84.4W 50 KT 60 MPH 120H 17/0600Z 32.2N 84.7W 35 KT 40 MPH...INLAND $$ Forecaster Cangialosi

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Tropical Storm Linda Forecast Discussion Number 8

2021-08-12 04:56:10| Tropical Depression LIDIA

Issued at 900 PM MDT Wed Aug 11 2021

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Tropical Depression Fred Forecast Discussion Number 10

2021-08-12 04:52:10| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Wed Aug 11 2021 409 WTNT41 KNHC 120252 TCDAT1 Tropical Depression Fred Discussion Number 10 NWS National Hurricane Center Miami FL AL062021 1100 PM EDT Wed Aug 11 2021 The center of Fred is estimated to be located over extreme eastern Haiti. This position is based on continuity with the previous forecast and a small low-level cyclonic circulation noted in cloud-drift wind vectors that were based on the last few GOES-16 high-resolution visible satellite images. A NOAA reconnaissance aircraft performed a quasi-synoptic surveillance mission this evening and released dropsondes while circumnavigating Hispaniola. Some of the dropsondes measured surface winds of 24-27 kt about 150 nmi north and northwest (in the Windward Passage) of the center, and these data support maintaining an intensity of 30 kt for this advisory. The main convective cloud mass has been displaced to the southeast of the low-level center due to the west-northwesterly vertical wind shear of about 20 kt. The initial motion estimate is 300/13 kt. The global and regional models remain in surprisingly good agreement on Fred maintaining a steady west-northwestward motion through 48-60 hours as a strong ridge remains entrenched over the western Atlantic during that time period. Thereafter, however, the NHC model guidance diverges significantly, with the now much weaker HWRF model taking Fred more westward, while the GFS and ECMWF models move the cyclone northwestward over the eastern Gulf of Mexico near or just offshore the Florida west coast; the UKMET model lies between these two track extremes. The weaker HWRF track has been discounted given the NHC forecast that Fred will remain vertically coherent and restrengthen after moving back over water. Thus, the new NHC track forecast is essentially just an update of the previous advisory track, and lies close to the NOAA-HCCA corrected-consensus model. NOTE: the aforementioned NOAA WP-3D reconnaissance aircraft has been releasing dropsondes from approximately the 450-mb level and has also been collecting tail-Doppler radar data. These data should have been assimilated into the 0000 UTC model runs, which hopefully will provide better track and intensity model forecasts for the next advisory package. Fred is forecast remain within a moderate to strong westerly to southwesterly vertical wind shear regime throughout the forecast period by almost all of the global and regional models. As a result, rapid strengthening is not expected after Fred moves back over water. There is one caveat, however, and that is the ECMWF model forecasting the shear to weaken to 5-10 kt during the 36-72 hour period, which could allow for a little more strengthening than what the official forecast is currently indicating. The new NHC intensity prediction is identical to the previous one owing to the expectation that some degree of westerly shear will be affecting Fred throughout the entire forecast period. The official forecast follows a blend of the IVCN and HCCA consensus intensity models. KEY MESSAGES: 1. Through early Thursday morning, heavy rainfall could lead to flash, urban, and small stream flooding, along with possible rapid river rises and potential mudslides in the Dominican Republic. 2. Tropical storm conditions are possible in northern Haiti, the Turks and Caicos, and the southeastern Bahamas tonight, and in portions of Cuba Thursday. 3. Beginning Friday, heavy rainfall could lead to areal, urban, and small stream flooding, and possible rapid river rises across southern Florida. Heavy rainfall associated with Fred will impact the remainder of Florida and parts of the Southeast this weekend and into next week. 4. There is a risk of tropical storm conditions beginning early Saturday in the Florida Keys and spreading northward along portions of the Florida west coast and the Florida Panhandle through Monday. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 19.5N 72.2W 30 KT 35 MPH...INLAND HISPANIOLA 12H 12/1200Z 20.4N 73.9W 30 KT 35 MPH...OVER WATER 24H 13/0000Z 21.6N 76.1W 30 KT 35 MPH 36H 13/1200Z 22.5N 78.1W 35 KT 40 MPH 48H 14/0000Z 23.5N 79.8W 35 KT 40 MPH 60H 14/1200Z 24.7N 81.2W 40 KT 45 MPH 72H 15/0000Z 26.2N 82.4W 45 KT 50 MPH 96H 16/0000Z 29.2N 84.2W 50 KT 60 MPH 120H 17/0000Z 31.7N 84.7W 35 KT 40 MPH...INLAND $$ Forecaster Stewart

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