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Tropical Storm Paulette Forecast Discussion Number 8

2020-09-08 22:30:40| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 08 2020 000 WTNT42 KNHC 082030 TCDAT2 Tropical Storm Paulette Discussion Number 8 NWS National Hurricane Center Miami FL AL172020 500 PM AST Tue Sep 08 2020 Shear has started to take a toll on Paulette's structure. Convection is again primarily limited to the northeast quadrant with little signs of banding. It is certainly possible that convection will expand again tonight when Paulette is farther removed from the diurnal convective minimum, but for the moment it does not look like further intensification is imminent. Dvorak classifications from TAFB and SAB are still T-3.5/55 kt, and that is the basis for the intensity estimate. If convection does increase tonight, Paulette will have a brief window for further strengthening before an expected increase in southerly shear on Wednesday. At a minimum, Paulette's intensity should then level off, and it will probably begin to weaken. Later this week or over the weekend Paulette will have an opportunity to restrengthen, depending on its interaction with an upper-level low expected to be just west of the cyclone. The spread in the guidance at that point is very high ranging from near dissipation to a category 2 hurricane. The NHC intensity forecast is mostly unchanged for now, but Paulette could certainly be much stronger or weaker over the weekend than currently forecast. There has been no change to the track forecast reasoning, and therefore little change to the track forecast itself. Paulette should gradually turn westward by late Wednesday and then back toward the northwest later this week as a ridge to its north builds and weakens over the next several days. The model spread is high, since there is still quite a bit of uncertainty in exactly how far west Paulette will make it before it turns northwestward. Confidence in the forecast beyond 72 h remains low. The NHC forecast track is based heavily on the HFIP Corrected Consensus (HCCA). FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 18.7N 44.3W 55 KT 65 MPH 12H 09/0600Z 19.2N 45.4W 60 KT 70 MPH 24H 09/1800Z 19.9N 47.2W 55 KT 65 MPH 36H 10/0600Z 20.3N 49.0W 55 KT 65 MPH 48H 10/1800Z 20.5N 50.6W 50 KT 60 MPH 60H 11/0600Z 20.7N 52.1W 50 KT 60 MPH 72H 11/1800Z 21.4N 53.2W 45 KT 50 MPH 96H 12/1800Z 23.5N 55.5W 45 KT 50 MPH 120H 13/1800Z 26.5N 59.0W 50 KT 60 MPH $$ Forecaster Zelinsky

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Tropical Storm Paulette Forecast Discussion Number 7

2020-09-08 16:33:08| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 08 2020 000 WTNT42 KNHC 081433 TCDAT2 Tropical Storm Paulette Discussion Number 7 NWS National Hurricane Center Miami FL AL172020 1100 AM AST Tue Sep 08 2020 Paulette's organization has noticeably improved since last night. The tropical storm is still sheared, with its outflow restricted to the southwest, however overnight AMSU imagery indicated that convection was beginning to wrap around the western portion of its circulation. The intensity estimate has been increased to 55 kt based on Dvorak estimates from TAFB and SAB. Paulette has manged to strengthen despite the shear, and some additional short-term strengthening is certainly possible. It is not out of the question that Paulette could become a hurricane, at least briefly. The global models indicate that the shear will increase on Wednesday, which should cause Paulette's intensity to level off, and more likely, decrease. The NHC intensity forecast is just above the intensity consensus for the first 3 days, out of respect for Paulette's recent intensification above most of the guidance. By the weekend, Paulette's strength will heavily depend on its exact orientation relative to an upper-level low that is expected to be located west or southwest of the tropical storm. Some restrengthening could occur then, but the NHC forecast just shows a steady intensity, near the middle of the guidance suite. Paulette is forecast to turn generally west-northwestward or westward tonight and Wednesday as a mid-level ridge builds to its north. The guidance then indicates that late this week Paulette will turn northwestward when the ridge weakens. Differences in Paulette's forward speed on Wednesday and Thursday could result in a very different track late in the period since it affects the point at which the tropical storm will turn northwestward. The NHC forecast is very close to the multi-model consensus throughout the 5-day period, but confidence in the forecast beyond 72 h is lower than normal due to high spread in the track guidance. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 18.4N 43.3W 55 KT 65 MPH 12H 09/0000Z 19.0N 44.2W 60 KT 70 MPH 24H 09/1200Z 19.8N 45.8W 60 KT 70 MPH 36H 10/0000Z 20.3N 47.8W 60 KT 70 MPH 48H 10/1200Z 20.6N 49.7W 55 KT 65 MPH 60H 11/0000Z 20.7N 51.2W 55 KT 65 MPH 72H 11/1200Z 21.2N 52.6W 50 KT 60 MPH 96H 12/1200Z 23.1N 55.4W 50 KT 60 MPH 120H 13/1200Z 26.0N 58.5W 50 KT 60 MPH $$ Forecaster Zelinsky

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Tropical Storm Rene Forecast Discussion Number 6

2020-09-08 16:32:07| National Hurricane Center (Atlantic)

Issued at 200 PM CVT Tue Sep 08 2020 000 WTNT43 KNHC 081431 TCDAT3 Tropical Storm Rene Discussion Number 6 NWS National Hurricane Center Miami FL AL182020 200 PM CVT Tue Sep 08 2020 Rene is starting to pull away from the Cabo Verde Islands, though some of the outer rainbands are affecting the far northwestern islands. Although the tropical storm has a well-defined circulation, the convective banding features have not become any better organized since yesterday. The satellite classifications are largely unchanged and range from 25 to 37 kt, and a recent ASCAT-B pass showed maximum winds in the 30-35 kt range. Based on all of this data, the initial intensity is again held at 35 kt. The tropical storm is moving westward at a faster pace of 14 kt. A mid-level ridge to the north of Rene is expected to build westward, which should cause the cyclone to move westward to west-northwestward at about the same forward speed during the next couple of days. After that time, the storm is expected to slow down and turn northwestward and then northward as it moves into a pronounced weakness in the ridge. Although the models agree on the overall scenario, there are notable differences in where and how sharply Rene will recurve with the GFS on the right side of the guidance and the ECMWF on the left. The NHC track forecast is adjusted a little to the right of the previous one, but still lies closer to the left side of the guidance envelope between the HCCA and TVCA consensus aids. Although Rene has not strengthened since yesterday, the models continue to suggest that the storm will steadily strengthen during the next few days while it moves over relatively warm 26-27 C waters and remains in environment of low wind shear and high moisture. Beyond that time, increasing southwesterly wind shear and drier air should end the strengthening trend and induce gradual weakening. The NHC intensity forecast is largely an update of the previous one and lies near the HCCA and IVCN models. Key Messages: 1. Rene is expected to produce tropical storm conditions across portions of the western Cabo Verde Islands for a few more hours. A Tropical Storm Warning remains in effect for those islands. 2. Rene will continue to bring locally heavy rainfall to portions of the western Cabo Verde Islands today. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 16.5N 26.5W 35 KT 40 MPH 12H 09/0000Z 16.8N 28.5W 35 KT 40 MPH 24H 09/1200Z 17.4N 31.1W 45 KT 50 MPH 36H 10/0000Z 18.3N 33.7W 55 KT 65 MPH 48H 10/1200Z 19.3N 36.2W 65 KT 75 MPH 60H 11/0000Z 20.5N 38.2W 70 KT 80 MPH 72H 11/1200Z 22.1N 39.8W 70 KT 80 MPH 96H 12/1200Z 26.5N 42.2W 60 KT 70 MPH 120H 13/1200Z 29.7N 42.0W 50 KT 60 MPH $$ Forecaster Cangialosi

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Tropical Storm Rene Forecast Discussion Number 5

2020-09-08 10:38:34| National Hurricane Center (Atlantic)

Issued at 800 AM CVT Tue Sep 08 2020 000 WTNT43 KNHC 080838 TCDAT3 Tropical Storm Rene Discussion Number 5 NWS National Hurricane Center Miami FL AL182020 800 AM CVT Tue Sep 08 2020 While Rene continues to have a well-defined circulation, satellite imagery indicates that the associated convection remains poorly organized. Various subjective and objective satellite intensity estimates are in the 30-35 kt range. Based on these, along with a 28 kt observation from Sal/GVAC, the initial intensity remains a possible generous 35 kt. The initial motion is westward or 280/13 kt. There is no change in the track forecast philosophy, as a westward motion is expected today, followed by a west-northwestward motion through Thursday as Rene rounds the southwestern periphery of a deep-layer subtropical ridge. On days 4 and 5, the cyclone is forecast to move more slowly northwestward to north-northwestward through a weakness in the aforementioned ridge. The track guidance has shifted a little eastward after 72 h, and the new track forecast is also nudged eastward during that time. Other than that, the new forecast track is similar to the previous track. It is unclear why the convection is currently so poorly organized, although land interaction with the Cabo Verde Islands is a possibility. Conditions generally appear favorable for strengthening during the next three days or so, and much of the intensity guidance forecasts Rene to become a hurricane in 2-3 days time even though the water temperatures gradually decrease along the forecast track. After 72 h, Rene is expected to reach both warmer water and strong westerly shear, with the latter expected to cause the storm to weaken. The new intensity forecast has only minor tweaks from the previous forecast and follows the trend of the intensity guidance. Key Messages: 1. Rene is expected to produce tropical storm conditions across portions of the Cabo Verde Islands today. A Tropical Storm Warning is in effect for those islands. 2. Rene will bring locally heavy rainfall to portions of the Cabo Verde Islands today. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 16.4N 24.9W 35 KT 40 MPH 12H 08/1800Z 16.7N 26.9W 35 KT 40 MPH 24H 09/0600Z 17.1N 29.5W 45 KT 50 MPH 36H 09/1800Z 17.9N 32.1W 55 KT 65 MPH 48H 10/0600Z 18.8N 34.7W 65 KT 75 MPH 60H 10/1800Z 19.8N 37.1W 70 KT 80 MPH 72H 11/0600Z 21.0N 39.0W 70 KT 80 MPH 96H 12/0600Z 24.5N 42.0W 65 KT 75 MPH 120H 13/0600Z 28.6N 42.9W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Storm Paulette Forecast Discussion Number 6

2020-09-08 10:35:33| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Sep 08 2020 000 WTNT42 KNHC 080835 TCDAT2 Tropical Storm Paulette Discussion Number 6 NWS National Hurricane Center Miami FL AL172020 500 AM AST Tue Sep 08 2020 GOES-16 Proxy-VIS and enhanced BD-curve infrared imagery reveals that Paulette's cloud pattern has continued to improve during the past several hours. Specifically, the developing inner core is much more symmetric with new bursts of deep convection (-76C cloud tops) near the surface circulation center. Subsequently, subjective and objective satellite intensity estimates support an initial intensity of 45 kt. The global models and the statistical-dynamical intensity guidance indicate increasing southwesterly shear commencing later today. So, only modest strengthening is shown in the NHC foreast during next 24 hours. On Friday, the shear stiffens and becomes less diffluent as the cyclone approaches the high amplitude mid-Atlantic TUTT. Therefore, Gradual weakening is expected to occur at that time. Beyond day 3, there are some mixed signals, specifically in the GFS/FV3 and ECMWF SHIPS output. The GFS/FV3 continues to indicate strong southwesterly shear through day 5 further weakening Paulette to a depression around day 4. The ECMWF SHIPS, however, shows a more southerly and diffluent upper wind pattern supporting reintensification after day 4. The intensity forecast sides with that latter solution and also agrees with the HCCA intensity multi-model indicating the same intensity trend. The initial motion is estimated to be northwestward, or 325/5 kt. The rather weak synoptic steering pattern consists of a large mid- to upper-level low just west of the Canary Islands and ridging to the northwest of the cyclone. During the next couple of days, the large-scale models show the upper low filling and lifting northeastward, allowing the subtropical ridge to build in behind the departing upper low from the western Atlantic. This change in the pattern should cause Paulette to turn west-northwestward on Wednesday and continue moving in this general motion through early Saturday. Through the remaining portion of the period, the global models indicate a major shortwave trough moving off of the northeast coast of the U.S. and breaking down the western extent of the subtropical ridge/Bermuda high. This growing weakness in the ridge should cause Paulette to turn toward the northwest early Sunday. The official track forecast is a little bit slower and to the right of the previous forecast after day 3, and is close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 18.1N 42.8W 45 KT 50 MPH 12H 08/1800Z 18.6N 43.6W 50 KT 60 MPH 24H 09/0600Z 19.5N 45.0W 55 KT 65 MPH 36H 09/1800Z 20.2N 46.9W 55 KT 65 MPH 48H 10/0600Z 20.5N 48.9W 55 KT 65 MPH 60H 10/1800Z 20.8N 50.4W 50 KT 60 MPH 72H 11/0600Z 21.3N 51.9W 50 KT 60 MPH 96H 12/0600Z 22.9N 54.9W 45 KT 50 MPH 120H 13/0600Z 25.4N 57.8W 50 KT 60 MPH $$ Forecaster Roberts

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