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Tropical Storm Rene Forecast Discussion Number 14

2020-09-10 16:38:12| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Sep 10 2020 000 WTNT43 KNHC 101438 TCDAT3 Tropical Storm Rene Discussion Number 14 NWS National Hurricane Center Miami FL AL182020 1100 AM AST Thu Sep 10 2020 Vertical shear appears to have lessened somewhat over Rene, with the estimated center more embedded within the convective cloud mass. The storm has also developed a better defined anticyclonic outflow pattern. Dvorak intensity estimates from both TAFB and SAB are 45 kt, and that will be used for the advisory intensity. Since the vertical shear is not expected to be strong for the next 48 hours or so, gradual strengthening is anticipated during that time, and Rene is forecast to become a hurricane by Saturday. This is in reasonable agreement with the latest intensity model consensus, IVCN. In the latter half of the forecast period, increased westerly shear over the tropical cyclone is expected, which should lead to weakening. Rene continues on a west-northwestward track, and is moving at about 285/10 kt. The tropical cyclone is currently located on the southwest side of a mid-level ridge over the eastern Atlantic. Over the next few days, Rene should move around the western periphery of this ridge and turn from a west-northwestward to a north-northwestward heading. Around the end of the forecast period, a high building to the northwest of the cyclone will likely cause a significant slowing of the forward speed. The official track forecast is a little left of the previous one to be in better agreement with the latest model consensus predictions. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 18.6N 35.8W 45 KT 50 MPH 12H 11/0000Z 19.0N 37.2W 50 KT 60 MPH 24H 11/1200Z 19.6N 39.3W 55 KT 65 MPH 36H 12/0000Z 20.4N 41.4W 60 KT 70 MPH 48H 12/1200Z 21.7N 43.6W 65 KT 75 MPH 60H 13/0000Z 23.1N 45.6W 65 KT 75 MPH 72H 13/1200Z 24.7N 47.2W 60 KT 70 MPH 96H 14/1200Z 27.6N 49.3W 50 KT 60 MPH 120H 15/1200Z 29.2N 50.3W 40 KT 45 MPH $$ Forecaster Pasch

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Tropical Storm Paulette Forecast Discussion Number 15

2020-09-10 16:38:10| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Sep 10 2020 000 WTNT42 KNHC 101438 TCDAT2 Tropical Storm Paulette Discussion Number 15 NWS National Hurricane Center Miami FL AL172020 1100 AM AST Thu Sep 10 2020 The highest winds in a recent scatterometer pass have decreased a little since last evening, and they remain embedded within deep convection which is displaced to the north of the center of circulation. Paulette's intensity is estimated to have decreased to 45 kt based on this ASCAT pass and Dvorak CI numbers of 3.0/45 kt from both TAFB and SAB. The sheared convection has been tugging Paulette's center northward at times, causing wobbles in the estimated longer-term west-northwestward motion of 295/9 kt. For the next 4 days or so, fluctuations in the strength of the subtropical ridge to the north of Paulette will cause the cyclone's trajectory to vary between west-northwest and northwest, with a peak in forward speed around day 3. At the end of the forecast period, a mid-latitude trough is expected to move across the northeastern United States, with a mid-tropospheric high becoming established over the central Atlantic. This should allow Paulette to begin to recurve over the western Atlantic, turning northward by day 5. The only notable change in the track guidance on this cycle was a slight westward shift among some of the models on days 4 and 5, and the NHC track forecast follows suit, lying close to the HFIP Corrected Consensus (HCCA) aid. Southwesterly shear has increased over the cyclone as expected, with the latest UW-CIMSS analysis now between 35 and 40 kt. SHIPS diagnoses suggest that the shear over Paulette should peak in about 12 hours, thus a little more weakening is anticipated over the next day or so. The shear is then forecast to gradually abate, and both the GFS and ECMWF versions of the SHIPS guidance show the shear magnitudes decreasing to 10 kt or less in 3-4 days. This more favorable environment, combined with a more unstable air mass and sea surface temperatures exceeding 29 degrees Celsius, are expected to allow Paulette to restrengthen and become a hurricane as it moves in the vicinity of Bermuda. The new NHC intensity forecast has been raised a bit between days 2 and 4 compared to the previous prediction, although it still lies below the intensity consensus, IVCN, and the HCCA solutions. Therefore, additional upward adjustments to the forecast intensity may be required later today. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 21.5N 49.1W 45 KT 50 MPH 12H 11/0000Z 21.8N 50.7W 45 KT 50 MPH 24H 11/1200Z 22.6N 52.6W 40 KT 45 MPH 36H 12/0000Z 23.8N 54.4W 40 KT 45 MPH 48H 12/1200Z 25.4N 56.3W 45 KT 50 MPH 60H 13/0000Z 26.9N 58.4W 50 KT 60 MPH 72H 13/1200Z 28.0N 61.0W 60 KT 70 MPH 96H 14/1200Z 30.0N 65.0W 70 KT 80 MPH 120H 15/1200Z 32.5N 65.0W 75 KT 85 MPH $$ Forecaster Berg

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Tropical Storm Rene Forecast Discussion Number 13

2020-09-10 10:38:43| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 10 2020 000 WTNT43 KNHC 100838 TCDAT3 Tropical Storm Rene Discussion Number 13 NWS National Hurricane Center Miami FL AL182020 500 AM AST Thu Sep 10 2020 Several recent microwave overpasses indicate that Rene continues to be affected by easterly shear, with the low-level center located near the eastern edge of the ongoing bursting convection. Various subjective and objective satellite intensity estimates are in the 35-45 kt range and have changed little since the last advisory. Based on that, the initial intensity remains 35 kt. The initial motion is west-northwestward or 285/9 kt. There is no change in the overall track forecast philosophy. Rene should move generally west-northwestward for the next couple of days, followed by a turn toward the northwest into a weakness in the subtropical ridge partly caused by Tropical Storm Paulette. Late in the forecast period, the track forecast becomes more problematic due to uncertainties in how much ridging will build north of Rene and how close it will be to the larger Paulette. The track guidance during this time shows increasing spread and some westward shift from the previous advisory. The new NHC forecast track is similar to the previous track through 72 h, then it lies to the left of the previous track at 96 and 120 h. However, at these times, it lies to the right of the various consensus models. The shear should gradually diminish during the next 48-60 h, and this should allow Rene to strengthen to or near hurricane strength. After that time, strong west-northwesterly shear is expected to cause gradual weakening despite the cyclone moving over increasing sea surface temperatures. The new official intensity forecast is unchanged from the previous forecast. It lies near the various intensity consensus models through 72 h, but is weaker than those models at 96 and 120 h. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 18.2N 34.8W 35 KT 40 MPH 12H 10/1800Z 18.6N 36.2W 40 KT 45 MPH 24H 11/0600Z 19.1N 38.1W 45 KT 50 MPH 36H 11/1800Z 19.8N 40.2W 50 KT 60 MPH 48H 12/0600Z 21.0N 42.2W 60 KT 70 MPH 60H 12/1800Z 22.4N 44.1W 65 KT 75 MPH 72H 13/0600Z 24.1N 45.7W 60 KT 70 MPH 96H 14/0600Z 27.0N 47.5W 50 KT 60 MPH 120H 15/0600Z 28.6N 49.0W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Paulette Forecast Discussion Number 14

2020-09-10 10:37:35| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 10 2020 000 WTNT42 KNHC 100837 TCDAT2 Tropical Storm Paulette Discussion Number 14 NWS National Hurricane Center Miami FL AL172020 500 AM AST Thu Sep 10 2020 Although Paulette's center of circulation has separated farther south from the cloud mass during the past several hours, the cyclone is still producing an area of deep convection consisting of -79C cold cloud tops. Earlier scatterometer data indicated surface winds of 45-50 kt in this region of coldest cloud tops, so it's reasonable to think that those winds are still present. Therefore, the initial intensity is held at 50 kt for this advisory. Both the ECMWF and FV3 SHIPS intensity models show the shear magnitude increasing to 35-40 kt today. As a result, Paulette is expected to begin weakening by this evening. Over the weekend, however, the shear is forecast to decrease gradually and shift from the southeast and become a bit more diffluent, which should allow for reintensification. Several of the skilled intensity guidance, including the aforementioned SHIPS, and the consensus models, HCCA and IVCN, now show Paulette as a hurricane in 4 days, or sooner (COAMPS-TC). The official intensity forecast is once again adjusted upward, and lies between the HCCA (a little higher) and the Decay SHIPS intensity guidance. The initial motion is estimated to be west-northwestward, or 290/9 kt and Paulette should continue in this general motion through Friday as a mid-tropospheric ridge temporarily builds over the central Atlantic in response to a mid- to upper-level trough, extending southwestward from the Azores Islands, weakening and lifting northeastward. By Saturday morning, a break in the aforementioned ridge develops due to a combination of mid- to upper-level low situated to the northwest of the cyclone and a mid-latitude shortwave trough moving off of the northeast U.S. This change in the synoptic steering pattern should cause the tropical cyclone to turn toward the northwest with an increase in forward speed. The NHC track forecast is close to the previous advisory, but a little faster beyond 48 hours, and is shifted to the left, closer to the HCCA and TVCN consensus models at days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 20.9N 49.0W 50 KT 60 MPH 12H 10/1800Z 21.3N 50.4W 50 KT 60 MPH 24H 11/0600Z 21.8N 52.4W 45 KT 50 MPH 36H 11/1800Z 22.8N 54.2W 40 KT 45 MPH 48H 12/0600Z 24.1N 55.9W 40 KT 45 MPH 60H 12/1800Z 25.7N 57.5W 45 KT 50 MPH 72H 13/0600Z 27.1N 59.4W 50 KT 60 MPH 96H 14/0600Z 29.7N 63.7W 65 KT 75 MPH 120H 15/0600Z 32.0N 64.9W 75 KT 85 MPH $$ Forecaster Roberts

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Tropical Storm Rene Forecast Discussion Number 12

2020-09-10 04:34:35| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 09 2020 000 WTNT43 KNHC 100234 TCDAT3 Tropical Storm Rene Discussion Number 12 NWS National Hurricane Center Miami FL AL182020 1100 PM AST Wed Sep 09 2020 Rene remains a sheared tropical cyclone, with modest mid-/upper-level easterly vertical wind shear of 12-15 kt undercutting the otherwise favorable outflow layer. The combination of the shear and intrusions of dry mid-level air have caused the convective pattern to continue to fluctuate since the previous advisory. Although a recent burst of deep convection has again pulsed near and to he west of the center, the intensity is being maintained at 35 kt based on a 09/2305Z ASCAT-A overpass indicating barely 34 kt winds in the northwest quadrant. The 34-kt wind radius was also expanded in that quadrant based on the ASCAT wind data. The initial motion remains west-northwestward motion or 285/11 kt. Under the influence of a mid-level ridge, Rene is expected to continue moving west-northward over the eastern Atlantic for the next few days. A weakness in the ridge is forecast to develop around 40W-45W longitude, which will be partly induced by Tropical Storm Paulette's circulation, causing Rene to slow down and turn toward the northwest and then north-northwest on 3-4 days. By day 5, Rene's northward motion is forecast to be blocked significantly by a building ridge to the north of the cyclone as TS Paulette moves farther away. It is possible that Rene could stall or even make a small looping motion if the storm gets trapped within the much larger ridge. The new NHC forecast is to the left or south of the previous advisory track, but not as far left as the consensus models or the preponderance of the remaining guidance. Rene's upper-level outflow is forecast to remain intact for the next 60 h or so, which would should allow for at least gradual strengthening during that time. The shear is forecast by both the GFS and the ECMWF models to decrease to near zero in the 36-48 h time frame, and that is when Rene should be able to take advantage of marginal sea-surface temperatures (SST) of 26.5C and modest mid-level humidity conditions, and obtain hurricane status in 48-60 h. Thereafter, strong west-northwesterly shear is expected to induce gradual weakening despite the cyclone moving over warmer SSTs of 27-28C. The official intensity forecast is similar to the GFS model intensity forecast, and lies below the simple consensus model IVCN and the corrected-consensus models HCCA and FSSE. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 18.0N 34.0W 35 KT 40 MPH 12H 10/1200Z 18.4N 35.5W 40 KT 45 MPH 24H 11/0000Z 18.9N 37.4W 45 KT 50 MPH 36H 11/1200Z 19.4N 39.3W 50 KT 60 MPH 48H 12/0000Z 20.5N 41.4W 60 KT 70 MPH 60H 12/1200Z 21.8N 43.2W 65 KT 75 MPH 72H 13/0000Z 23.5N 45.1W 60 KT 70 MPH 96H 14/0000Z 26.8N 46.5W 50 KT 60 MPH 120H 15/0000Z 28.3N 47.6W 40 KT 45 MPH $$ Forecaster Stewart

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