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Tropical Storm Rene Forecast Discussion Number 20

2020-09-12 04:41:44| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 11 2020 000 WTNT43 KNHC 120241 TCDAT3 Tropical Storm Rene Discussion Number 20 NWS National Hurricane Center Miami FL AL182020 1100 PM AST Fri Sep 11 2020 Deep convection has persisted near the center of Rene since this afternoon and a couple of earlier microwave overpasses suggest that there has been an increase in banding over the southwestern portion of the circulation. Despite what appears to be an increase in organization, recent ASCAT data indicated that this has not translated into an increase in intensity. The scatterometer data still supports an initial wind speed of 35 kt. Environmental conditions are forecast to generally be conducive for some strengthening over the next 12-24 hours, however with Rene continuing to struggle to intensify the NHC wind speed prediction has again been reduced during the that time. By 36-48 hours, Rene is expected to move beneath an area of strong upper-level west-northwesterly flow, and this increase in shear is expected to cause weakening. The ECMWF and GFS models significantly weaken Rene after 72 hours, with the ECMWF showing dissipation before the end of the forecast period. For now, the official forecast calls for Rene to weaken to a tropical depression by day 4, but it is possible that the system will degenerate into a trough of low pressure before day 5. Rene is moving west-northwestward or 295/12 kt. The cyclone should turn toward the northwest as it moves around the western portion of a mid-level ridge over the eastern Atlantic. In a couple of days, a mid-level high is predicted to build to the northwest of Rene, which should cause the cyclone to slow down and turn westward, and then west-southwestward later in the forecast period. The track guidance is in fairly good agreement and the various consensus aids remained close to the previous official forecast. Therefore, the new NHC forecast is essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 21.4N 42.4W 35 KT 40 MPH 12H 12/1200Z 22.4N 44.0W 35 KT 40 MPH 24H 13/0000Z 24.1N 45.8W 40 KT 45 MPH 36H 13/1200Z 25.7N 47.0W 40 KT 45 MPH 48H 14/0000Z 26.8N 47.6W 40 KT 45 MPH 60H 14/1200Z 27.1N 47.8W 35 KT 40 MPH 72H 15/0000Z 26.8N 48.4W 35 KT 40 MPH 96H 16/0000Z 25.9N 50.9W 30 KT 35 MPH 120H 17/0000Z 24.8N 54.0W 30 KT 35 MPH $$ Forecaster Brown

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Tropical Depression Nineteen Forecast Discussion Number 1

2020-09-11 22:59:32| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Sep 11 2020 148 WTNT44 KNHC 112059 TCDAT4 Tropical Depression Nineteen Discussion Number 1 NWS National Hurricane Center Miami FL AL192020 500 PM EDT Fri Sep 11 2020 GOES-16 1-minute satellite data show that the system near the Bahamas that we have been monitoring for the past couple of days has quickly organized into a tropical depression. Very deep convection has formed near the center, and the 1-min data now shows enough north and northwest flow to indicate that a well-defined center is present. The initial wind speed is 30 kt in agreement with recent ship data. It is uncertain whether the large burst of convection over the center will continue and cause the depression to become a tropical storm before reaching Florida. However, since it is only a 5 kt increase from the current intensity, it is possible that tropical storm conditions could still occur along the southeast Florida coast late tonight, and a tropical storm watch has been issued. Otherwise, after the system reaches the eastern Gulf of Mexico, steady intensification is expected through the weekend due to expected light wind shear and very warm water. Some increase in shear could occur over the northern Gulf of Mexico but that is uncertain at this time. The first forecast will stay conservative and only show a peak intensity of 60 kt in 3 to 4 days, but do not be surprised if that is revised upward on later forecasts once other models better initialize the depression. An uncertain estimate of the initial motion is 285/7. Strong ridging over the southeastern United States is expected to steer the cyclone to the west-northwest then northwest as a mid-latitude trough erodes the western side of the ridge over the weekend. The forecast gets tricky after that because the bulk of the guidance suggests the trough isn't deep enough to recurve the system, and instead it gets left behind, moving slowly westward early next week due to weak ridging over the southern Plains. The NHC forecast is near the corrected-consensus guidance. The uncertainty in the track forecast is much larger than normal after 48 hours, as small changes in the forecast steering flow could result in this system moving over the northern Gulf Coast faster and to the northeast of what is shown here. As a result, the risk of seeing direct impacts from this system extends well outside the cone of uncertainty, even more so than usual in this case. 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 in the Tampa Bay area. 2. Tropical storm conditions are possible tonight along the southeast Florida coast where a Tropical Storm Watch is in effect. 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 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 tonight and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 25.4N 79.0W 30 KT 35 MPH 12H 12/0600Z 25.7N 80.1W 30 KT 35 MPH 24H 12/1800Z 26.2N 81.9W 30 KT 35 MPH 36H 13/0600Z 27.3N 83.8W 35 KT 40 MPH 48H 13/1800Z 28.4N 85.2W 45 KT 50 MPH 60H 14/0600Z 29.1N 86.3W 55 KT 65 MPH 72H 14/1800Z 29.5N 87.4W 60 KT 70 MPH 96H 15/1800Z 30.0N 89.0W 60 KT 70 MPH 120H 16/1800Z 31.0N 91.0W 25 KT 30 MPH...INLAND $$ Forecaster Blake

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Tropical Storm Rene Forecast Discussion Number 19

2020-09-11 22:52:03| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 11 2020 062 WTNT43 KNHC 112051 TCDAT3 Tropical Storm Rene Discussion Number 19 NWS National Hurricane Center Miami FL AL182020 500 PM AST Fri Sep 11 2020 Deep convection has increased over the western semicircle of the circulation and is re-forming near the center. Based on a blend of subjective Dvorak classifications and ADT values from UW-CIMSS, the current intensity estimate remains at 35 kt. Hopefully we will get a scatterometer pass over the system soon to give a better intensity estimate. Some strengthening is anticipated during the next day or so, but increasing shear should halt the intensification process, and bring about weakening, thereafter. The official intensity forecast is above the latest model consensus. Rene continues to move west-northwestward and should gradually turn to the right while it moves around the western periphery of a mid-level high pressure system for the next couple of days. In the latter half of the forecast period, a blocking high to the north and northwest of Rene should force the cyclone to turn toward the west and west-southwest. The new official track forecast has been shifted to the southwest of the previous one in 3-5 days, following the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 20.7N 41.1W 35 KT 40 MPH 12H 12/0600Z 21.7N 42.8W 40 KT 45 MPH 24H 12/1800Z 23.3N 44.8W 45 KT 50 MPH 36H 13/0600Z 24.9N 46.4W 45 KT 50 MPH 48H 13/1800Z 26.4N 47.3W 45 KT 50 MPH 60H 14/0600Z 27.0N 47.4W 40 KT 45 MPH 72H 14/1800Z 27.0N 48.0W 40 KT 45 MPH 96H 15/1800Z 26.5N 50.0W 35 KT 40 MPH 120H 16/1800Z 25.0N 53.0W 35 KT 40 MPH $$ Forecaster Pasch

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Tropical Storm Paulette Forecast Discussion Number 20

2020-09-11 22:50:37| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 11 2020 000 WTNT42 KNHC 112050 TCDAT2 Tropical Storm Paulette Discussion Number 20 NWS National Hurricane Center Miami FL AL172020 500 PM AST Fri Sep 11 2020 Paulette inconveniently fell in a gap between all three ASCAT passes this morning, so we haven't gotten any better handle on the cyclone's intensity since last evening's pass. However, Dvorak classifications have not budged, so maintaining the initial intensity of 55 kt seems sound. In addition, although an AMSR microwave pass from around 17 UTC still showed the system being sheared, it also revealed a ragged mid-level eye feature. Since the shear is expected to abate to less than 10 kt by 48 hours, Paulette is likely to intensify, possibly significantly so, and it is now forecast to become a hurricane on Saturday. The intensification trend is expected to continue through day 4, and Paulette has the potential to be a dangerous hurricane when it makes its closest approach to Bermuda on Monday. Paulette's forecast peak intensity (on day 4) has been nudged up slightly, lying near the SHIPS and HCCA guidance, but still a little below the latest HWRF simulation. Paulette has picked up some speed and is now moving toward the northwest (310 degrees) at 11 kt. The track forecast reasoning has not changed since this morning. Paulette should maintain a motion toward the northwest or west-northwest during the next 2 to 3 days to the south of a weakening subtropical ridge. By day 3, a longwave trough is forecast to move across the northeastern United States, eroding the ridge eastward, and causing Paulette to recurve sharply toward the north and northeast in the vicinity of Bermuda on Monday. After that time, Paulette is forecast to become embedded in the mid-latitude flow and accelerate northeastward toward the north Atlantic. The spread in the track guidance has continued to tighten up, which increases the confidence in the official track forecast. The updated forecast has been shifted slightly westward around the time that Paulette will be near Bermuda, and it is embedded among the usually-reliable GFS, ECMWF, and HCCA model solutions. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane during the next couple of days and make its closest approach to the island on Monday. A prolonged period of strong winds, storm surge, and heavy rainfall on Bermuda beginning Sunday night is becoming more likely, and a hurricane watch could be required for the island tonight or 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 11/2100Z 24.6N 53.7W 55 KT 65 MPH 12H 12/0600Z 25.9N 55.3W 60 KT 70 MPH 24H 12/1800Z 27.5N 57.5W 65 KT 75 MPH 36H 13/0600Z 28.7N 59.8W 70 KT 80 MPH 48H 13/1800Z 29.8N 62.3W 80 KT 90 MPH 60H 14/0600Z 31.1N 64.5W 85 KT 100 MPH 72H 14/1800Z 32.6N 65.3W 90 KT 105 MPH 96H 15/1800Z 36.0N 62.0W 95 KT 110 MPH 120H 16/1800Z 39.0N 56.0W 85 KT 100 MPH $$ Forecaster Berg

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Tropical Storm Paulette Forecast Discussion Number 19

2020-09-11 16:44:59| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 11 2020 000 WTNT42 KNHC 111444 TCDAT2 Tropical Storm Paulette Discussion Number 19 NWS National Hurricane Center Miami FL AL172020 1100 AM AST Fri Sep 11 2020 Despite what is being analyzed as roughly 40 kt of deep-layer southwesterly shear, Paulette's center is embedded beneath the cirrus canopy of a strong convective burst to the north. Recent microwave images do confirm, however, that the center remains displaced from the convection. We have not yet received new scatterometer data over Paulette, and since the structure has not degraded from overnight, the initial intensity remains 55 kt. This is in best agreement with the Dvorak estimate from TAFB. Paulette appears to have turned toward the northwest (305/9 kt) based on center fixes over the past 12 hours. A weakness in the subtropical ridge is beginning to develop to the north of Paulette, which should allow the cyclone to maintain a motion toward the northwest or west-northwest during the next 3 days. After that time, a longwave trough forecast to move across the northeastern United States is expected to erode the ridge eastward, causing Paulette to recurve sharply toward the north and northeast in the vicinity of Bermuda on days 4 and 5. Except for some minor speed differences, the track models agree on this general trajectory and have less east-to-west spread during the recurvature phase than they did yesterday. The GFS, ECMWF, HCCA, and Florida State Superensemble aids all lie along the western side of the guidance envelope at the time of recurvature, and as a result the new NHC track has been nudged a little west of the previous prediction during that period in deference to those normally reliable models. The shear affecting Paulette is forecast to abate over the next 48 hours while the storm also moves over warmer ocean waters and into a more unstable environment. Given the cyclone's hardiness in the face of the ongoing shear, Paulette is unlikely to have problems responding to the improving environment. Paulette is now forecast to become a hurricane in 36 hours, which is supported by the latest dynamical hurricane models, the superensemble aids, and the IVCN intensity consensus. Continued strengthening is anticipated after 36 hours, with Paulette likely to reach a peak intensity in 4-5 days. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane this weekend and make its closest approach to the island on Monday. While the exact details of Paulette's track and intensity near the island are not yet known, the risk of strong winds, storm surge, and heavy rainfall on Bermuda continues to increase. 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 11/1500Z 23.6N 52.2W 55 KT 65 MPH 12H 12/0000Z 24.6N 53.7W 55 KT 65 MPH 24H 12/1200Z 26.1N 55.5W 60 KT 70 MPH 36H 13/0000Z 27.6N 57.5W 65 KT 75 MPH 48H 13/1200Z 28.9N 59.9W 75 KT 85 MPH 60H 14/0000Z 30.2N 62.5W 80 KT 90 MPH 72H 14/1200Z 31.6N 64.3W 85 KT 100 MPH 96H 15/1200Z 34.5N 63.5W 90 KT 105 MPH 120H 16/1200Z 37.0N 58.0W 90 KT 105 MPH $$ Forecaster Berg

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