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Tropical Depression Nineteen Forecast Discussion Number 3

2020-09-12 11:03:10| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Sep 12 2020 958 WTNT44 KNHC 120903 TCDAT4 Tropical Depression Nineteen Discussion Number 3 NWS National Hurricane Center Miami FL AL192020 500 AM EDT Sat Sep 12 2020 Surface observations and Doppler radar data indicate that Tropical Depression Nineteen was close to tropical storm strength when it moved ashore in Miami-Dade county just after 06Z. The central pressure had dropped to near 1004 mb, and the radar showed winds of 45-50 kt above the surface just to the northeast of the center, associated with a strong convective burst. However, there were no surface observations of 35-kt sustained winds, and the highest reported gusts were in the 35-40 kt range. Based on the available data, the initial intensity remains 30 kt. It should be noted that since landfall, the strong convective burst near the low-level center has weakened considerably. The cyclone has turned left during the past several hours, and the initial motion is a somewhat uncertain 270/8 kt. The subtropical ridge extending from the southeastern United States eastward over the Atlantic should steer the cyclone generally west-northwestward through Sunday. After that time, the ridge is forecast to weaken due to an approaching mid-latitude trough. This should result in a northwestward motion through from Sunday night into the middle portion of next week, with the cyclone expected to reach the northern Gulf coast around the 96 h point. The latest track guidance now has the cyclone responding more strongly to the trough and turning northward by 120 h. The new forecast track is shifted a little south of the previous track through 72 h based on the initial position and motion. At 120 h, the new track is nudged to the east of the old track, but it still lies to the west of the consensus models. The depression is currently experiencing some northerly vertical wind shear, and the latest global model runs are showing more shear affecting the system as it crosses the Gulf of Mexico than earlier. However, since the cyclone is going to be over very warm sea surface temperatures and in a moist environment, the intensity guidance still shows it strengthening to near hurricane strength, or stronger, before it reaches the northern Gulf coast. Due to the uncertainty about the amount of shear, the new intensity forecast has only minor adjustments from the previous forecast. However, it lies below the various intensity consensus models. Users are reminded to not to focus on the exact details of the track or intensity forecast as the average NHC track error at 96 h is around 150 miles and the average intensity error is around 15 mph. In addition, winds, storm surge, and rainfall hazards will extend far from the center. KEY MESSAGES: 1. Tropical Depression Nineteen is expected to produce isolated to scattered flash flooding across portions of west-central and southern Florida and prolong existing minor river flooding across Central Florida through Sunday. Scattered flash flooding is also possible across portions of the central Gulf Coast Sunday through Tuesday morning. 2. Tropical storm conditions are possible by Sunday night in portions of the Florida Panhandle, where a Tropical Storm Watch has been issued. Wind gusts to tropical-storm force could occur over portions of the southern Florida Peninsula today. 3. The system is forecast to strengthen to near hurricane intensity by early next week as it moves across the northeastern Gulf of Mexico. Dangerous impacts from storm surge, wind, and heavy rainfall will be possible along the Gulf Coast from the Florida Panhandle to southeastern Louisiana late this weekend and early next week. Residents in these areas should monitor the progress of this system and updates to the forecast, as Storm Surge, Tropical Storm or Hurricane watches could be issued later today. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 25.6N 80.7W 30 KT 35 MPH...INLAND 12H 12/1800Z 26.1N 82.0W 30 KT 35 MPH...OVER WATER 24H 13/0600Z 26.9N 83.8W 35 KT 40 MPH 36H 13/1800Z 27.9N 85.4W 40 KT 45 MPH 48H 14/0600Z 28.7N 86.6W 50 KT 60 MPH 60H 14/1800Z 29.3N 87.7W 60 KT 70 MPH 72H 15/0600Z 29.6N 88.5W 60 KT 70 MPH 96H 16/0600Z 30.5N 90.0W 55 KT 65 MPH...INLAND 120H 17/0600Z 31.5N 90.5W 25 KT 30 MPH...INLAND $$ Forecaster Beven

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Tropical Storm Rene Forecast Discussion Number 21

2020-09-12 10:44:14| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 12 2020 000 WTNT43 KNHC 120844 TCDAT3 Tropical Storm Rene Discussion Number 21 NWS National Hurricane Center Miami FL AL182020 500 AM AST Sat Sep 12 2020 Deep convection associated with Rene appears to have lost some organization overnight. Although there have been several pulsating bursts of convection overnight, the convection that was persistent over the center during the evening is now confined to the southern portion of the circulation. A blend of the latest subjective and objective satellite intensity estimates yields an initial intensity of 35 kt, but this could be generous. ASCAT data later this morning should help to determine if Rene is still a topical storm. Mid-level dry air appears to be the primary reason why Rene has struggled to strengthen over the past few days, and although the shear is expected to remain low today, the dry air is likely to prevent strengthening. On Sunday, Rene is forecast to approach an area of strong west-northwesterly flow aloft, and this increase is shear is likely to cause the cyclone to weaken. Most of the global models continue to significantly weaken Rene early next week, and both the ECMWF and GFS suggest that the cyclone will degenerate into a trough of low pressure by days 4 or 5. The NHC forecast continues to maintain Rene as a tropical cyclone throughout the forecast period, but if the current trends it is becoming unlikely that Rene will survive as a tropical cyclone for the entire 5-day period. Rene has turned northwestward and is now moving at 305/13 kt. A northwestward motion around the western periphery of a mid-level ridge over the eastern Atlantic should continue for another 12 to 24 hours, but by late Sunday Rene is forecast to slow down as ridge of high pressure builds to the northwest and north of the cyclone. Later in the period, Rene is forecast to turn westward and then southwestward under the influence of the building ridge. The track guidance remains in fairly good agreement, and no significant changes to the official forecaster were required. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 22.5N 43.5W 35 KT 40 MPH 12H 12/1800Z 23.7N 44.9W 35 KT 40 MPH 24H 13/0600Z 25.4N 46.3W 35 KT 40 MPH 36H 13/1800Z 26.6N 47.3W 35 KT 40 MPH 48H 14/0600Z 27.2N 47.7W 30 KT 35 MPH 60H 14/1800Z 27.1N 48.1W 30 KT 35 MPH 72H 15/0600Z 26.7N 49.1W 30 KT 35 MPH 96H 16/0600Z 25.5N 52.0W 30 KT 35 MPH 120H 17/0600Z 24.7N 55.0W 30 KT 35 MPH $$ Forecaster Brown

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Tropical Storm Paulette Forecast Discussion Number 22

2020-09-12 10:43:44| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 12 2020 000 WTNT42 KNHC 120843 TCDAT2 Tropical Storm Paulette Discussion Number 22 NWS National Hurricane Center Miami FL AL172020 500 AM AST Sat Sep 12 2020 Conventional satellite imagery shows that the cyclone's cloud pattern has improved during the past several hours and that Paulette maybe on the cusp of becoming a hurricane very soon. An Advanced Technology Microwave Sounder (ATMS) overpass suggested that the cyclone has a much less vertical tilt and deep convective banding is developing in the south and east portions of Paulette. The subjective and objective satellite intensity T-numbers haven't changed from 6 hours ago, and the initial intensity is held at 60 kt. The UW-CIMSS shear analysis reveals some decrease in the shear magnitude and the upper wind pattern has become much more diffluent. The ECMWF/FV3 SHIPS and the large-scale models indicate that the shear will relax soon, and Paulette should become a hurricane today and further strengthen to a major hurricane early Tuesday. The SHIPS statistical-dynamical model indicates this scenario occuring earlier, Monday evening. The official intensity forecast is nudged slightly higher than the previous one and is close to the the HFIP Corrected Consensus Approach intensity model. It is also important to note that the average NHC intensity errors are around 10-15 kt at 48-72 h, the range at which Paulette will likely be nearest to Bermuda. The initial motion is estimated to be northwestward, or 310/15 kt. A mid-tropospheric ridge/Bermuda high north of the cyclone should continue to build across the western Atlantic and steer Paulette west-northwestward for the next 36 hours. Afterward, a turn toward the northwest to north-northwest with a significant increase in forward speed is expected early Monday and Monday evening in response to an approaching mid-latitude major shortwave trough. The track guidance suite remains tightly clustered with just some minor forward speed differences beyond day 3, so it's quite certain that Paulette will move near Bermuda early Monday, though it's a little too early to specify the exact closest approach. The NHC track forecast is close to the previous advisory and once again is based on the various multi-model guidance. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane on Sunday and Monday. A prolonged period of strong winds, storm surge, and heavy rainfall on Bermuda beginning Sunday night is becoming increasingly likely. A tropical storm warning and a hurricane watch have been issued for the island. 2. Swells produced by Paulette are affecting portions of the Leeward Islands and will continue to spread westward to the Greater Antilles, the Bahamas, Bermuda, and the southeastern United States through the weekend. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 26.8N 56.1W 60 KT 70 MPH 12H 12/1800Z 28.0N 58.0W 70 KT 80 MPH 24H 13/0600Z 29.2N 60.5W 75 KT 85 MPH 36H 13/1800Z 30.3N 62.9W 80 KT 90 MPH 48H 14/0600Z 31.8N 64.8W 85 KT 100 MPH 60H 14/1800Z 33.5N 65.2W 90 KT 105 MPH 72H 15/0600Z 35.2N 63.2W 95 KT 110 MPH 96H 16/0600Z 38.2N 56.9W 95 KT 110 MPH 120H 17/0600Z 41.5N 49.7W 80 KT 90 MPH $$ Forecaster Roberts

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Tropical Storm Paulette Forecast Discussion Number 21

2020-09-12 04:53:37| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 11 2020 000 WTNT42 KNHC 120253 TCDAT2 Tropical Storm Paulette Discussion Number 21 NWS National Hurricane Center Miami FL AL172020 1100 PM AST Fri Sep 11 2020 Paulette remains sheared and asymmetric, with all its deep convection north of its low-level center of circulation. Despite the shear, ASCAT-B data that just arrived showed maximum winds near or just over 55 kt. Since that instrument tends to under-sample the maximum winds, the initial intensity is increased to 60 kt. An upper-level low located to the west of Paulette is responsible for the southerly shear currently affecting the cyclone. Global model forecasts suggest that the shear will continue for another day or so, and only slight strengthening is likely through that period. By Sunday, the upper-level low will move farther southwest and the tropical cyclone will encounter a very favorable upper-air pattern. Paulette will likely strengthen further in response, possibly at a fast rate. All of the intensity guidance indicates that Paulette will be a hurricane when it nears Bermuda early Monday, and it could approach major hurricane strength early next week. The NHC intensity forecast has not changed since the last advisory. It is worth mentioning that Paulette could experience a period of slow development for the next 24 hours, followed by quick intensification, rather than the more steady strengthening shown by the NHC forecast. It is also important to note that the average NHC intensity errors are around 10-15 kt at 48-72 h, the range at which Paulette will likely be nearest to Bermuda. Paulette has jogged slightly right of track during the past few hours, but the overall NHC forecast track is not different from the previous advisory. A building mid-level ridge to the north of Paulette will likely steer the tropical storm generally west-northwestward or northwestward for the next 2-3 days. The cyclone is then expected to turn northeastward and accelerate in that direction ahead of a mid-latitude trough. The model spread remains relatively low, especially for the first few days. Confidence is high that Paulette will move near Bermuda early Monday, though it is still too soon to specify exactly how close it will get. The NHC forecast is based heavily on the TVCA and HCCA consensus aids and is not far from any of the global model forecast. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane on Sunday and Monday. A prolonged period of strong winds, storm surge, and heavy rainfall on Bermuda beginning Sunday night is becoming more likely. A tropical storm watch is in effect and a hurricane watch could be required for the island early Saturday. 2. Swells produced by Paulette are affecting portions of the Leeward Islands and will continue to spread westward to the Greater Antilles, the Bahamas, Bermuda, and the southeastern United States into the weekend. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 25.8N 54.8W 60 KT 70 MPH 12H 12/1200Z 27.1N 56.5W 65 KT 75 MPH 24H 13/0000Z 28.5N 58.8W 65 KT 75 MPH 36H 13/1200Z 29.6N 61.2W 70 KT 80 MPH 48H 14/0000Z 30.7N 63.7W 80 KT 90 MPH 60H 14/1200Z 32.1N 65.1W 85 KT 100 MPH 72H 15/0000Z 33.8N 65.0W 90 KT 105 MPH 96H 16/0000Z 37.0N 60.0W 95 KT 110 MPH 120H 17/0000Z 40.0N 54.0W 85 KT 100 MPH $$ Forecaster Zelinsky

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Tropical Depression Nineteen Forecast Discussion Number 2

2020-09-12 04:43:39| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Sep 11 2020 000 WTNT44 KNHC 120243 TCDAT4 Tropical Depression Nineteen Discussion Number 2 NWS National Hurricane Center Miami FL AL192020 1100 PM EDT Fri Sep 11 2020 Doppler radar data from Miami and satellite images indicate that the depression is gradually becoming better organized. The low-level center is estimated to be near the northwestern edge of the main area of deep convection due to some northerly wind shear. Surface observations and satellite classifications support holding the initial intensity at 30 kt. The minimum pressure appears to be a little lower than before, now 1007 mb. The tropical depression is moving west-northwestward at about 7 kt. A subtropical ridge extending from the southeast U.S. to the western Atlantic should steer the depression west-northwestward across south Florida tonight and Saturday morning and then over the eastern Gulf of Mexico late Saturday and Sunday. After that time, the ridge is forecast to weaken due to an approaching trough, but the trough is not expected to be strong enough to cause the cyclone to turn northward. Instead, the models suggest that a slow west-northwestward motion very near the northern Gulf coast is likely during the early and middle portions of next week. Although the models all show a relatively similar scenario, there is a fair amount of spread by the time the system nears the northern Gulf coast. The NHC track forecast lies roughly near the middle of the guidance envelope close to the consensus aids. Several of the local National Weather Service forecast offices across the southeast U.S. will be launching weather balloons four times per day, which should provide the models with excellent data in hopes to provide better track guidance during the next couple of days. Since the depression is expected to move over very warm SSTs, once it reaches the eastern Gulf of Mexico tomorrow, and remain in an environment of low wind shear and high moisture, gradual strengthening seems likely. The models suggest that there could be an increase in westerly shear around the time the cyclone is forecast to move inland along the northern Gulf coast in about 4 days. Based on these expected environmental conditions, strengthening is forecast during the next few days, and the NHC intensity forecast follows the trend of the IVCN and HCCA models. The depression will likely be at or near hurricane strength when it reaches the northern Gulf coast. Users are reminded to not to focus on the exact details of the track or intensity forecast as the average NHC track error at 96 h is around 150 miles and the average intensity error is around 15 mph. In addition, winds, storm surge, and rainfall hazards will extend far from the center. KEY MESSAGES: 1. Heavy rainfall is expected to produce isolated flash flooding over portions of central and southern Florida and prolong existing minor river flooding across central Florida. 2. Tropical storm conditions are possible overnight and early Saturday along the southeast Florida coast where a Tropical Storm Watch is in effect. Tropical storm conditions are possible by Sunday night in portions of the Florida Panhandle, where a Tropical Storm Watch has been issued. 3. The system is forecast to strengthen to near hurricane intensity by early next week as it moves across the northeastern Gulf of Mexico. Dangerous impacts from storm surge, wind, and heavy rainfall will be possible along the Gulf Coast from the Florida Panhandle to southeastern Louisiana late this weekend and early next week. Residents in these areas should monitor the progress of this system and updates to the forecast, as Storm Surge, Tropical Storm or Hurricane watches could be issued on Saturday. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 25.7N 79.8W 30 KT 35 MPH 12H 12/1200Z 26.0N 81.0W 30 KT 35 MPH...INLAND 24H 13/0000Z 26.8N 82.9W 35 KT 40 MPH 36H 13/1200Z 27.9N 84.6W 40 KT 45 MPH 48H 14/0000Z 28.8N 85.9W 45 KT 50 MPH 60H 14/1200Z 29.3N 86.9W 55 KT 65 MPH 72H 15/0000Z 29.7N 87.7W 60 KT 70 MPH 96H 16/0000Z 30.2N 89.5W 60 KT 70 MPH...INLAND 120H 17/0000Z 31.3N 90.9W 25 KT 30 MPH...INLAND $$ Forecaster Cangialosi

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