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Tropical Storm Victor Forecast Discussion Number 6
2021-09-30 22:43:09| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Sep 30 2021 000 WTNT45 KNHC 302042 TCDAT5 Tropical Storm Victor Discussion Number 6 NWS National Hurricane Center Miami FL AL202021 500 PM AST Thu Sep 30 2021 Victor has been relatively steady in strength during the past several hours. Satellite images continue to show that the storm has a large circulation with numerous curved bands surrounding the center. However, recent microwave images indicate that the cyclone has yet to develop a well-defined inner core, which is likely why the system has not strengthened much despite the favorable environmental conditions. The Dvorak classifications are again unchanged and range from 35 to 45 kt, and on this basis, the initial intensity is held at 40 kt. Victor is still moving west-northwestward, or 290 degrees, at 12 kt. The storm is forecast to continue on that same general track for about another day as it remains on the south side of a deep-layer ridge over the subtropical eastern Atlantic. By late Friday, a mid- to upper-level low is expected to form over the central Atlantic, and that feature should erode the western portion of the ridge. As a result, Victor is expected to turn northwestward by the weekend and then northward by early next week when it is forecast to move in the flow between the ridge and the low. The GFS has shifted westward this cycle and is now not far from the ECMWF track. The new NHC forecast track is nudged westward toward a consensus of the GFS, ECMWF, UKMET, and HMON models. The standard consensus aids could be too far to the east since the latest run of the HWRF, which is a member of those models, is a significant outlier to the east. As mentioned above, although the storm has been in favorable conditions for strengthening during the past day or so, it has not taken full advantage likely due to its broad structure. The favorable environment for Victor should persist for about another 24 hours, so gradual strengthening is possible during that time period. However, by the weekend, the models show Victor moving into a region of moderate to strong southwesterly shear and a progressively drier airmass. These negative factors for the storm along with slightly cooler SSTs should cause Victor to lose strength this weekend and early next week. In fact, some of the models suggest that Victor could dissipate by the end of the forecast period. The new NHC intensity forecast is again a little lower than the previous one, trending toward the HCCA, IVCN, and IVDR consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 9.9N 30.0W 40 KT 45 MPH 12H 01/0600Z 10.6N 31.4W 45 KT 50 MPH 24H 01/1800Z 11.6N 33.1W 55 KT 65 MPH 36H 02/0600Z 12.9N 34.6W 50 KT 60 MPH 48H 02/1800Z 14.5N 36.2W 45 KT 50 MPH 60H 03/0600Z 16.4N 38.0W 40 KT 45 MPH 72H 03/1800Z 18.9N 40.0W 35 KT 40 MPH 96H 04/1800Z 23.6N 42.7W 30 KT 35 MPH 120H 05/1800Z 28.0N 42.9W 30 KT 35 MPH $$ Forecaster Cangialosi
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Hurricane Sam Forecast Discussion Number 32
2021-09-30 16:55:31| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 30 2021 000 WTNT43 KNHC 301455 TCDAT3 Hurricane Sam Discussion Number 32 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Thu Sep 30 2021 Sam continues to look quite impressive on satellite images, with a 20-25 n mi wide eye surrounded by very deep convection. The system's convective banding features and upper-level anticyclonic outflow also remain well-defined, with particularly strong outflow to the northwest and north. Subjective and objective Dvorak intensity estimates have not changed significantly since earlier this morning, so the advisory intensity will remain at 125 kt. Interestingly, aircraft observations show that Sam has been a little stronger than indicated by satellite-derived intensity estimates, which underscores the value of aerial reconnaissance of tropical cyclones. Another Air Force Hurricane Hunter aircraft is scheduled to investigate the hurricane later today. Sam should continue to move over waters of high oceanic heat content and within a low-shear atmospheric environment for the next 24 hours or so. Thus, it could still strengthen a little today and tonight. By 48 hours, decreasing SSTs and increasing shear should lead to a gradual weakening trend. Around day 5, global model fields suggest that Sam will be merging with a baroclinic zone and transition into a large and powerful extratropical cyclone over the north Atlantic. The official intensity forecast is in good agreement with the HCCA corrected consensus model prediction. The hurricane is moving a little faster toward the northwest, or at about 320/11 kt. During the next couple of days, a gradual turn toward the north is likely as Sam rounds the western end of a large subtropical anticyclone over the eastern and central Atlantic. Thereafter, Sam is forecast to move generally northeastward in the flow between the anticyclone and a trough near Atlantic Canada. The NHC forecast is very similar to a consensus of the typically reliable GFS and ECMWF predictions, with a little bit of smoothing around days 3-4. Although the core of Sam is forecast to pass east of Bermuda early Saturday, the tropical-storm-force wind field is forecast to expand and could pass very close to the island beginning late Friday night or early Saturday. Therefore, a Tropical Storm Watch is in effect for Bermuda. Key Messages: 1. Swells generated by Sam will impact the Northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next few days. Swells are expected to reach Bermuda and the Bahamas by Friday, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. Tropical storm conditions are possible on Bermuda beginning Friday night or early Saturday, and a Tropical Storm Watch has been issued for that island. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 22.6N 60.0W 125 KT 145 MPH 12H 01/0000Z 24.4N 60.8W 130 KT 150 MPH 24H 01/1200Z 27.2N 61.7W 125 KT 145 MPH 36H 02/0000Z 30.2N 61.6W 115 KT 130 MPH 48H 02/1200Z 32.7N 60.8W 105 KT 120 MPH 60H 03/0000Z 34.9N 59.2W 95 KT 110 MPH 72H 03/1200Z 36.9N 57.0W 90 KT 105 MPH 96H 04/1200Z 40.0N 51.0W 80 KT 90 MPH 120H 05/1200Z 44.5N 45.5W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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Tropical Storm Victor Forecast Discussion Number 5
2021-09-30 16:54:32| National Hurricane Center (Atlantic)
Issued at 200 PM CVT Thu Sep 30 2021 000 WTNT45 KNHC 301454 TCDAT5 Tropical Storm Victor Discussion Number 5 NWS National Hurricane Center Miami FL AL202021 200 PM CVT Thu Sep 30 2021 Victor remains a sprawling tropical storm with numerous curved bands surrounding the center. The associated convection remains most organized on the storm's west side. The latest Dvorak estimates are largely unchanged and range from 35 to 45 kt. In addition, an ASCAT-B pass from around 12Z showed maximum winds in the 35-40 kt range. Based on all of this data, the initial intensity is held at 40 kt. The ASCAT data also showed that the wind field is quite broad with tropical-storm-force winds extending about 90 n mi north of the center. Victor is still moving west-northwestward, or 290 degrees, at 12 kt. The storm is forecast to continue on that same general track for another day or so as it remains on the south side of a deep-layer ridge over the subtropical eastern Atlantic. By late Friday, a mid- to upper-level low is expected to form over the central Atlantic, and that feature should erode the western portion of the ridge. As a result, Victor is expected to turn northwestward by the weekend and then northward early next week when it is forecast to move in the flow between the ridge and the low. The model tracks have converged compared to yesterday, but the ECMWF remains the slowest and westernmost solution and the HWRF is still the easternmost model. The NHC track forecast is nudged to the west of the previous one and lies close to the various consensus aids and is in fair agreement with the GFS. The storm has about another 36 hours in conducive environmental conditions of very low wind shear, a moist mid-level airmass, and warm 28-29 degree C SSTs. Therefore, intensification seems likely during that time period, but given the broad nature of the system's wind field, Victor will likely gain strength slowly during that time period. However, in a couple of days, the models show a significant increase in southwesterly shear and a progressively drier airmass. These negative factors for the storm along with slightly cooler SSTs should cause Victor to lose strength. In fact, some of the models suggest that Victor could dissipate by the end of the forecast period. The new NHC intensity forecast is a little lower than the previous one. It should be noted that although this forecast no longer explicitly shows Victor becoming a hurricane, it could occur in a day or two before conditions become hostile. This forecast lies near the high end of the model guidance. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 9.5N 28.9W 40 KT 45 MPH 12H 01/0000Z 10.2N 30.4W 50 KT 60 MPH 24H 01/1200Z 11.1N 32.3W 60 KT 70 MPH 36H 02/0000Z 12.4N 34.0W 60 KT 70 MPH 48H 02/1200Z 13.9N 35.5W 55 KT 65 MPH 60H 03/0000Z 15.7N 37.2W 50 KT 60 MPH 72H 03/1200Z 17.9N 39.0W 45 KT 50 MPH 96H 04/1200Z 23.2N 41.8W 35 KT 40 MPH 120H 05/1200Z 28.0N 42.4W 30 KT 35 MPH $$ Forecaster Cangialosi
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Hurricane Sam Forecast Discussion Number 31
2021-09-30 10:56:25| National Hurricane Center (Atlantic)
Issued at 500 AM AST Thu Sep 30 2021 113 WTNT43 KNHC 300856 TCDAT3 Hurricane Sam Discussion Number 31 NWS National Hurricane Center Miami FL AL182021 500 AM AST Thu Sep 30 2021 Sam is a very impressive hurricane in infrared satellite imagery this morning. The 25-nm-wide eye remains very distinct and is surrounded by a ring of convection with cloud tops around -65C. The outflow is also well established in all quadrants. An Air Force Reserve Hurricane Hunter aircraft that performed three eyewall penetrations overnight has reported peak 700-mb flight-level winds of 139 kt in the northeastern, southeastern, and eastern eyewall, and peak SFMR surface winds of 119 kt. These data still support an initial wind speed of 125 kt. Sam's minimum pressure has fallen a few millibars since the NOAA aircraft mission last evening. The latest estimated pressure from dropsonde data gathered by the Air Force is 937 mb. NOAA buoy 41044 has recently reported a peak one-minute wind of 68 kt with a gust to 86 kt in the northeastern eyewall of Sam. The buoy has also reported peak seas of 40 ft. Sam could still strengthen a little today as it continues to move over a warm ocean eddy and remains in low vertical wind shear conditions. After that time, difficult-to-predict eyewall cycles however, could cause some fluctuations in intensity. After 48 hours, gradually decreasing SSTs and ocean heat content are likely to cause a more definitive weakening trend, with a faster rate of weakening likely after day 3. Sam is forecast to complete its extratropical transition by day 5, and it is predicted by the global model guidance to become a large and powerful extratropical low over the north Atlantic. Sam is moving northwestward or 320/10 kt. The track forecast reasoning is again unchanged from the previous advisory. Sam will move northwestward, and then northward around the western portion of a subtropical ridge during the next 48 hours. After that time, Sam is predicted to turn northeastward between the ridge and a large mid-latitude trough over the northeastern United States. As that trough lifts northeastward by day 3, Sam is forecast to continue on a northeastward heading, but it is not likely to accelerate as much as a typical recurving tropical cyclone over the north-central Atlantic. The dynamical model guidance remains in excellent agreement through 72 hours, but there is increasing spread after that time. The latest runs of the GFS and ECMWF models have come into somewhat better agreement at days 3 through 5, and the NHC track forecast is near the consensus of those typically reliable models. Although the core of Sam is forecast to pass east of Bermuda early Saturday, the tropical-storm-force wind field is forecast to expand and could pass very close to the island beginning late Friday night or early Saturday. Therefore, the Bermuda Weather Service has issued a Tropical Storm Watch for Bermuda. Key Messages: 1. Swells generated by Sam will impact the Northern Leeward Islands and the Greater Antilles, including Puerto Rico, during the next few days. Swells are expected to reach Bermuda and the Bahamas by Friday, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. 2. Tropical storm conditions are possible on Bermuda beginning Friday night or early Saturday, and a Tropical Storm Watch has been issued for that island. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 21.5N 59.1W 125 KT 145 MPH 12H 30/1800Z 23.0N 60.2W 130 KT 150 MPH 24H 01/0600Z 25.6N 61.4W 125 KT 145 MPH 36H 01/1800Z 28.4N 61.8W 120 KT 140 MPH 48H 02/0600Z 31.1N 61.3W 115 KT 130 MPH 60H 02/1800Z 33.5N 59.9W 105 KT 120 MPH 72H 03/0600Z 35.5N 58.0W 95 KT 110 MPH 96H 04/0600Z 38.7N 52.6W 80 KT 90 MPH 120H 05/0600Z 44.3N 45.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Tropical Storm Victor Forecast Discussion Number 4
2021-09-30 10:42:56| National Hurricane Center (Atlantic)
Issued at 800 AM CVT Thu Sep 30 2021 000 WTNT45 KNHC 300842 TCDAT5 Tropical Storm Victor Discussion Number 4 NWS National Hurricane Center Miami FL AL202021 800 AM CVT Thu Sep 30 2021 Victor is gradually getting better organized. AMSR2 microwave data from 0300 UTC showed that the low-level circulation has become more defined, with most convective banding features located west and southwest of the center. Victor's intensity is now estimated to be 40 kt based on Dvorak estimates of T3.0 and T2.5 from TAFB and SAB, respectively, and objective numbers from UW-CIMSS around 40 kt. Victor's vector is toward the west-northwest (290 degrees) at 11 kt, and this heading should continue for the next 36 hours while the storm is located to the south a deep-layer ridge located over the subtropical eastern and central Atlantic. In about 2 days, a mid- to upper-level low is forecast to develop over the central Atlantic, causing Victor to curve around the western periphery of the ridge, which gets shunted eastward between the Azores and the Canary Islands. The track models are in generally good agreement on this scenario, and most of them are clustered tightly among each other. Two notable exceptions, which are discounted at this time, are the HWRF and ECMWF models. The HWRF, which is stronger than the other models, is way off to the east, while the ECMWF lies off to the south and west, a tendency that we've observed recently with other storms in the deep tropics. The NHC track forecast is not changed much from the previous iteration and lies close to the GFS, HCCA, Florida State Superensemble, and TVCA solutions. If the low-level circulation is in fact becoming better defined as shown by microwave imagery, Victor should be able to continue strengthening for the next couple of days in an environment of low vertical shear and over warm waters of roughly 28 degrees Celsius. The NHC intensity forecast is near the upper end of the guidance during this period and continues to show Victor reaching hurricane strength in about 36 hours. Once the aforementioned mid- to upper-level low forms, strong southerly to southwesterly deep-layer shear is expected to develop over Victor and induce a weakening trend in about 3 days. The intensity forecast has been lowered a bit during the latter part of the forecast period given the trends in the intensity models, but it is not as low as the HCCA and IVCN aids. Interestingly, many of the global models suggest that the shear could be so strong that Victor might weaken to a depression or even degenerate into a remnant low by day 5. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 8.7N 27.3W 40 KT 45 MPH 12H 30/1800Z 9.4N 28.8W 50 KT 60 MPH 24H 01/0600Z 10.2N 30.6W 60 KT 70 MPH 36H 01/1800Z 11.2N 32.3W 65 KT 75 MPH 48H 02/0600Z 12.6N 33.8W 65 KT 75 MPH 60H 02/1800Z 14.4N 35.3W 60 KT 70 MPH 72H 03/0600Z 16.6N 37.0W 55 KT 65 MPH 96H 04/0600Z 22.0N 40.2W 40 KT 45 MPH 120H 05/0600Z 27.3N 41.9W 35 KT 40 MPH $$ Forecaster Berg
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