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Remnants of Ten Forecast Discussion Number 6

2020-08-02 04:38:56| National Hurricane Center (Atlantic)

Issued at 200 AM CVT Sun Aug 02 2020 000 WTNT45 KNHC 020238 TCDAT5 Remnants Of Ten Discussion Number 6 NWS National Hurricane Center Miami FL AL102020 200 AM CVT Sun Aug 02 2020 Scatterometer data around 2130 UTC confirmed that the system north of the Cabo Verde islands no longer has a well-defined center. The scatterometer data showed that the southwest semicircle of the system consists of only light and variable winds, and the strongest winds associated with the system have decreased to around 20 kt. The system lacks deep convection and a combination of cool underlying water and a dry surrounding environment will prevent regeneration. This is the last NHC advisory on this system. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 19.5N 25.0W 20 KT 25 MPH...REMNANTS OF TEN 12H 02/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Isaias Forecast Discussion Number 19

2020-08-01 22:52:24| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sat Aug 01 2020 000 WTNT44 KNHC 012052 TCDAT4 Tropical Storm Isaias Discussion Number 19 NWS National Hurricane Center Miami FL AL092020 500 PM EDT Sat Aug 01 2020 The last data received from a previous Air Force Reserve reconnaissance aircraft, along with recent satellite and radar imagery, indicate that Isaias has weakened to a tropical storm due to a combination of shear, dry air and interaction with Andros Island earlier today. The initial intensity of 60 kt is based on SFMR surface wind speeds of near 60 kt in the northeastern quadrant on the last flight. A new reconnaissance mission into the cyclone is currently ongoing and will provide new data concerning the Isaias' intensity. The initial motion estimate is 315/09 kt. After making a slight west-northwestward jog a few hours ago after convection significantly weakened, Isaias appears to have returned to its base northwestward course. The new NHC model guidance is tightly packed but has shifted slightly westward, with some of the more reliable models now showing landfall along the east-central Florida coast in about 24 hours. Earlier NOAA G-IV jet dropsonde data and 12Z upper-air data reveal that the surface to 700 mb ridge extending east-west across central and northern Florida remains intact whereas the 500-300 mb ridge has completely eroded. The result is that lower level ridge will cause Isaias to slow its forward motion to northwestward at 6-8 kt during the next 36 hours. By 48 hours, the erosion of the ridge due to an approaching shortwave trough will allow the cyclone to move northward, followed by a gradual increase in forward speed toward the northeast on days 3-5. The new NHC track forecast was nudged slightly closer to the Florida east-central coast through 24 hours, with no significant changes made to the previous forecast after 36 hours. A combination of Isaias moving over the warm Gulfstream waters during the convective maximum period and increasing frictional convergence due to land interaction with Florida should lead to an increase in deep convection near and over the center, as shown by simulated satellite imagery from the ECMWF model. As a result, Isaias is forecast to regain hurricane status tonight, as shown by the HWRF and HMON model fields. By 36 hours and beyond, the global models are in good agreement that an approaching mid- to upper-level trough will increase southwesterly vertical wind shear, which should result in gradual weakening until Isais becomes an extratropical cyclone in about 96 hours. The new NHC intensity forecast is closest to the HMON in 12 hours and closely follows the IVCN and HCCA consensus models after 36 hours. Key Messages: 1. Hurricane conditions and dangerous storm surge will continue in portions of the northwest Bahamas tonight. 2. Hurricane conditions are expected along portions of the Florida east coast on Sunday with tropical storm conditions expected to begin tonight. Preparations to protect life and property should be rushed to completion. 3. Dangerous storm surge is possible along the Florida east coast from Jupiter Inlet to Ponte Vedra Beach where water rises of 2 to 4 feet above ground level are possible along the immediate coastline and adjacent waterways. Residents there should follow advice given by local emergency officials. 4. Isaias will produce heavy rains and potentially life-threatening flash flooding in the Bahamas, and flash and urban flooding, especially in low-lying and poorly drained areas, along the East Coast of the United States. Minor river flooding and isolated moderate river flooding is possible across portions of the Carolinas and Virginia early next week. 5. Tropical storm watches and warnings are in effect for portions of the United States East Coast from northeast Florida to South Carolina. Additional watches and warnings will likely be issued tonight and Sunday as Isaias is expected to move northward near or over the southeast and mid-Atlantic coasts early next week. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 25.1N 78.7W 60 KT 70 MPH 12H 02/0600Z 26.1N 79.4W 65 KT 75 MPH 24H 02/1800Z 27.4N 80.1W 65 KT 75 MPH 36H 03/0600Z 28.8N 80.7W 60 KT 70 MPH 48H 03/1800Z 30.7N 80.6W 55 KT 65 MPH 60H 04/0600Z 33.4N 79.1W 50 KT 60 MPH 72H 04/1800Z 37.4N 76.3W 45 KT 50 MPH...INLAND 96H 05/1800Z 45.4N 68.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 06/1800Z 50.7N 57.9W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Depression Ten Forecast Discussion Number 5

2020-08-01 22:34:24| National Hurricane Center (Atlantic)

Issued at 800 PM CVT Sat Aug 01 2020 000 WTNT45 KNHC 012034 TCDAT5 Tropical Depression Ten Discussion Number 5 NWS National Hurricane Center Miami FL AL102020 800 PM CVT Sat Aug 01 2020 The depression is barely a tropical cyclone. Most of the deep convection from the burst earlier in the day has now dissipated and the circulation appears to be losing definition. The initial intensity is held at 25 kt based on the ASCAT data from several hours ago. Since the cyclone is over cool waters and in a dry environment, significant deep convection is unlikely to return. Therefore, the depression will likely become a remnant low tonight and open into a trough shortly thereafter. The weak and shallow system has turned to the left recently, with the latest initial motion estimated to be 305/11 kt. A general west-northwest motion is expected until the system dissipates a couple of hundred miles north of the northern-most Cabo Verde Islands tonight or on Sunday. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 19.2N 23.5W 25 KT 30 MPH 12H 02/0600Z 19.9N 25.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 02/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Isaias Forecast Discussion Number 18

2020-08-01 17:00:22| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sat Aug 01 2020 000 WTNT44 KNHC 011500 TCDAT4 Hurricane Isaias Discussion Number 18 NWS National Hurricane Center Miami FL AL092020 1100 AM EDT Sat Aug 01 2020 Data from an Air Force Reserve reconnaissance aircraft around 1410 UTC indicated that the center of the eye of Isaias was located along the southern coast of northern Andros Island about 15 nmi south-southwest of Andros Town. The eye appearance in Bahamas and aircraft radar data, along with the visual reports from the flight crew, has gone from nearly closed a few hours ago to open in the southwestern quadrant more recently. However, the diameter of the eye has been has been holding steady between 20-22 nmi, an indication that Isaias has been able to fight off some modest southwesterly wind shear. The initial intensity has been lowered to 70 kt based on maximum 700-mb flight-level winds of 77 kt, which equals about 70-kt surface wind speed, and the central pressure fluctuating between 987-990 mb. The initial motion estimate remains 315/10 kt. The latest NHC model guidance is now tightly packed about the previous 18-h worth of official track forecasts, and as a result, no significant changes were made to the previous advisory track. The global and regional models have come into much better agreement compared to 24 hours ago in taking Isaias northwestward slowly for the next 36 h or so, and moving the center near or keeping it just offshore the east-central Florida coast. By 48 hours, the hurricane is expected to turn northward around the western portion of the Bermuda-Azores ridge that will slowly be eroded by an approaching mid-level shortwave trough currently situated over the central United States. By 60 h and beyond, the aforementioned trough is expected to gradually accelerate Isaias northeastward near or along the coast from South Carolina to New England. The new NHC track forecast is basically an extension of the previous one, and lies very close to an average of the simple consensus model TVCA, and the corrected- consensus models NOAA-HCCA and FSSE. In the near term, Isaias could weaken a little bit this afternoon while passing over northern Andros Island. However, the still impressive vertical structure of the cyclone should allow for some re-strengthening after the center moves back over the warm Gulf Stream by this evening. The current SHIPS analyzed westerly vertical wind shear of 25 kt could be too high due to the model incorporating some of the storm's outflow. The models forecast the shear to weaken somewhat over the next 36 h while Isaias is moving over the Gulf Stream, and the 06Z UKMET shows Isaias moving underneath a 200-mb anticyclone, which would normally favor some strengthening. Given all of these factors, the official forecast maintains a steady intensity through Monday night. Slow weakening is forecast when Isais encounters more significant southwesterly vertical wind shear ahead of a strong upper-level trough that will be approaching the U.S. east coast on days 3-5. Key Messages: 1. Hurricane conditions and dangerous storm surge will continue in portions of the northwest Bahamas today and tonight. 2. Hurricane conditions are expected along portions of the Florida east coast by late tonight and Sunday. Preparations to protect life and property should be rushed to completion. 3. Dangerous storm surge is possible along the Florida east coast from Jupiter Inlet to Ponte Vedra Beach where water rises of 2 to 4 feet above ground level are possible along the immediate coastline and adjacent waterways. Residents there should follow advice given by local emergency officials. 4. Isaias will produce heavy rains and potentially life-threatening flash flooding in the Bahamas, and flash urban flooding, especially in low-lying and poorly drained areas, in eastern Florida, and from the Carolinas to the mid-Atlantic and Northeast U.S. Minor river flooding is possible across portions of the Carolinas and Virginia early next week. 5. Tropical storm watches and warnings are in effect for portions of the northeast Florida and southern Georgia coasts. Additional watches and warnings will likely be issued later today and Sunday along the U.S. east coast as the risk of wind, heavy rainfall, and storm surge impacts continues to increase. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 24.7N 77.9W 70 KT 80 MPH 12H 02/0000Z 25.7N 78.8W 70 KT 80 MPH 24H 02/1200Z 27.1N 79.7W 70 KT 80 MPH 36H 03/0000Z 28.5N 80.3W 70 KT 80 MPH 48H 03/1200Z 30.1N 80.4W 65 KT 75 MPH 60H 04/0000Z 32.6N 79.4W 60 KT 70 MPH 72H 04/1200Z 36.0N 76.9W 50 KT 60 MPH...INLAND 96H 05/1200Z 43.3N 69.7W 45 KT 50 MPH...OVER WATER 120H 06/1200Z 49.0N 57.9W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Depression Ten Forecast Discussion Number 4

2020-08-01 16:32:50| National Hurricane Center (Atlantic)

Issued at 200 PM CVT Sat Aug 01 2020 000 WTNT45 KNHC 011432 TCDAT5 Tropical Depression Ten Discussion Number 4 NWS National Hurricane Center Miami FL AL102020 200 PM CVT Sat Aug 01 2020 The center of the depression is mostly exposed this morning with deep convection remaining only over the northwest portion of the circulation. A recent ASCAT overpass showed a small area of winds of 20 to 25 kt in the northern semicircle. Based on this data, the initial intensity has been lowered to 25 kt. The persistent convection has likely bought a little more time for the depression to survive. However, the cyclone is forecast to remain over SSTs of about 24 to 25 C for the next day or so. This should cause the convection to gradually decrease, causing the depression to become a remnant low by tonight. An alternative scenario is that the low could open into a trough before the convection dissipates. The depression is moving northwest at around 12 kt. A turn to the west-northwest is expected later today as the cyclone pivots around a large mid-level gyre to its southwest. This west-northwest motion should continue until the system dissipates. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 18.6N 22.2W 25 KT 30 MPH 12H 02/0000Z 19.8N 23.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 02/1200Z...DISSIPATED $$ Forecaster Latto

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