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Tropical Storm Sally Forecast Discussion Number 10

2020-09-14 04:54:19| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sun Sep 13 2020 542 WTNT44 KNHC 140254 TCDAT4 Tropical Storm Sally Discussion Number 10 NWS National Hurricane Center Miami FL AL192020 1000 PM CDT Sun Sep 13 2020 Sally is gradually getting better organized. Satellite images show that deep convection has increased near the center, and the cyclone is now a little more symmetric and vertically aligned compared to earlier today. The Air Force Hurricane Hunters are currently investigating Sally, and so far they have found maximum 850-mb flight-level winds of 54 kt and maximum believable SFMR winds of 49 kt, which support the 50-kt initial intensity. Reports from the aircraft indicate that the center of Sally has jogged to the northeast, with the latest 12-hour motion estimated to be 305/7 kt. The global models show a trough exiting the northeast U.S. tomorrow and a ridge building to the north of Sally, which should cause the storm to resume a west-northwest motion at a relatively slow pace on Monday. By Monday night and Tuesday, the ridge is forecast to slide southeastward as another trough develops over the south-central U.S. This change in the pattern should cause Sally to slow down even more and gradually turn to the north and then the northeast. The new NHC tack forecast is slower and east of the previous one based on the initial position/motion and the latest models. However, the official forecast still lies west of the latest consensus aids, so further adjustments may be necessary overnight. While the current forecast shows landfall along the northern Gulf coast in 36 to 48 hours, the bottom line is that Sally is expected to be a slow- moving tropical cyclone near and over the northern Gulf Coast during the next few days. The upper-level low that was producing northwesterly shear over Sally is moving away, resulting in a more favorable upper-level wind pattern for strengthening. These more conducive winds aloft combined with the very warm Gulf of Mexico waters and a moist air mass should allow the cyclone to steadily strengthening until Sally crosses the coast in 36 to 48 hours. The NHC intensity forecast is largely an update of the previous one and lies near the high end of the model guidance. After landfall, rapid weakening is forecast, and Sally is expected to become a tropical depression by 72 hours and dissipate in about 5 days. The eastward shift in the track forecast necessitates the extension of the hurricane warning eastward to the Mississippi/Alabama border. KEY MESSAGES: 1. It is too early to determine where Sally's center will move onshore given the uncertainty in the timing and location of Sally's northward turn near the central Gulf Coast. Users should not focus on the details of the official forecast track, since NHC's average forecast error at 48 hours is around 80 miles, and dangerous storm surge, rainfall, and wind hazards will extend well away from the center. 2. An extremely dangerous and life-threatening storm surge is expected for areas outside the southeastern Louisiana Hurricane and Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to the Alabama/Florida border, where a Storm Surge Warning is in effect. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are expected by late Monday within portions of the Hurricane Warning area from Morgan City, Louisiana, to the Mississippi/Alabama border, including Metropolitan New Orleans, with tropical storm conditions likely to begin Monday. Preparations should be rushed to completion in those areas. 4. Sally could continue to produce flash flooding across central and northern Florida and prolong existing minor river flooding across west-central Florida through Monday. Widespread significant flash flooding and minor to isolated major river flooding is likely across southeastern Louisiana, Mississippi, and Alabama through the middle of the week. Flooding impacts are expected to spread farther across the Southeast U.S. through the week. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 28.2N 86.2W 50 KT 60 MPH 12H 14/1200Z 28.6N 87.3W 60 KT 70 MPH 24H 15/0000Z 29.0N 88.3W 70 KT 80 MPH 36H 15/1200Z 29.4N 89.0W 80 KT 90 MPH 48H 16/0000Z 30.3N 89.4W 70 KT 80 MPH...INLAND 60H 16/1200Z 31.2N 89.1W 45 KT 50 MPH...INLAND 72H 17/0000Z 32.1N 88.3W 30 KT 35 MPH...INLAND 96H 18/0000Z 33.6N 85.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 19/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Twenty Forecast Discussion Number 6

2020-09-14 04:49:51| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 13 2020 000 WTNT45 KNHC 140249 TCDAT5 Tropical Depression Twenty Discussion Number 6 NWS National Hurricane Center Miami FL AL202020 1100 PM AST Sun Sep 13 2020 The depression continues to march west-northwestward with little change in its structure so far. Scatterometer data near 00Z revealed that the system is still elongated southwest to northeast with maximum winds near 30 kt. Convection has become a little more concentrated to the southwest of the depression's center during the past few hours, so perhaps this is a sign that it will start getting organized soon. As long as the depression remains disorganized, only minimal strengthening is likely. However, once the system comes together, all indications are that it will strengthen, perhaps significantly so. The cyclone still has several days to strengthen within a low-shear/high-SST environment, and even the global models explicitly forecast the system to become a hurricane. The NHC intensity forecast is unchanged and still brings the depression to major hurricane strength by the middle of the week. Some of the dynamical hurricane models indicate it could strengthen faster than that, so this forecast could wind up being conservative. The depression appears to be moving generally west-northwestward. A large mid-level ridge over the central Atlantic should keep the cyclone on this general heading for the next couple of days. After that, the ridge is forecast to move north and east, and the strengthening cyclone should turn toward the northwest in response. While the exact details vary from model to model, all of the dynamical track guidance supports this general scenario. The NHC forecast is based heavily on the model consensus and lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 13.0N 39.0W 30 KT 35 MPH 12H 14/1200Z 13.5N 41.2W 35 KT 40 MPH 24H 15/0000Z 13.9N 43.7W 45 KT 50 MPH 36H 15/1200Z 14.4N 45.9W 55 KT 65 MPH 48H 16/0000Z 15.0N 47.3W 70 KT 80 MPH 60H 16/1200Z 16.0N 48.7W 80 KT 90 MPH 72H 17/0000Z 17.2N 50.0W 90 KT 105 MPH 96H 18/0000Z 20.0N 52.4W 100 KT 115 MPH 120H 19/0000Z 23.0N 55.0W 100 KT 115 MPH $$ Forecaster Zelinsky

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Hurricane Paulette Forecast Discussion Number 29

2020-09-14 04:46:56| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 13 2020 000 WTNT42 KNHC 140246 TCDAT2 Hurricane Paulette Discussion Number 29 NWS National Hurricane Center Miami FL AL172020 1100 PM AST Sun Sep 13 2020 The eye of Paulette is steadily nearing Bermuda. Although it has appeared slightly ragged at times in IR imagery, radar imagery from Bermuda and the NOAA P3 show that the eye and eyewall of Paulette are very well defined in all quadrants but the southwest. The NOAA hurricane hunter plane measured peak flight-level winds of 89 kt (which adjust to 80 kt at the surface) and SFMR winds of 70 kt. Taking an average of those supports the initial intensity of 75 kt. The minimum pressure measured by the NOAA aircraft in its last pass through the eye was 976 mb. The track, intensity, and wind radii forecasts for Paulette are very similar to the last advisory. Given its improved structure over the past day or so and its favorable upper-air environment, some additional strengthening appears likely as Paulette approaches Bermuda during the next few hours. Further intensification is possible after the hurricane accelerates northeastward away from Bermuda and Paulette is expected to be at or near major hurricane strength on Tuesday. By the end of the forecast period, weakening is expected as Paulette interacts with a mid-latitude trough and begins to lose its tropical characteristics. The NHC intensity forecast is generally just above the intensity consensus but is within the tightly clustered guidance envelope at all times. Confidence in the track forecast is quite high and the models are in excellent agreement on Paulette's future for the next few days. The hurricane will approach Bermuda and turn northward tomorrow, then accelerate northeastward through the middle of the week. A slower eastward or even southeastward motion is possible by Friday when a large cut-off mid- to upper-level low over the eastern Atlantic is forecast to begin influencing Paulette's track. Key Messages: 1. The eye of Paulette will approach Bermuda early Monday and hurricane conditions are expected to begin on the island within the next few hours. A prolonged period of strong winds, storm surge, and very heavy rainfall will likely continue into Monday afternoon. 2. Swells produced by Paulette are affecting portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 31.4N 64.0W 75 KT 85 MPH 12H 14/1200Z 32.8N 64.7W 85 KT 100 MPH 24H 15/0000Z 34.9N 63.6W 95 KT 110 MPH 36H 15/1200Z 37.1N 60.1W 100 KT 115 MPH 48H 16/0000Z 39.3N 55.2W 95 KT 110 MPH 60H 16/1200Z 41.6N 49.6W 85 KT 100 MPH 72H 17/0000Z 43.8N 44.0W 75 KT 85 MPH 96H 18/0000Z 46.0N 37.5W 55 KT 65 MPH 120H 19/0000Z 43.5N 34.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Tropical Storm Karina Forecast Discussion Number 5

2020-09-14 04:31:52| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sun Sep 13 2020 000 WTPZ41 KNHC 140231 TCDEP1 Tropical Storm Karina Discussion Number 5 NWS National Hurricane Center Miami FL EP162020 800 PM PDT Sun Sep 13 2020 Karina's satellite presentation is not terribly impressive, with the deep convection sheared well south of what appears to be a somewhat elongated low-level center by 15 to 20 kt of northerly shear. The subjective Dvorak Final-T numbers have decreased a little in the last 6 hours, but overall a blend of the objective and subjective satellite estimates yields an intensity of 40 kt for this advisory. Karina only has a limited window for strengthening, with SSTs forecast to cool to 26C along the forecast track within 36 hours. With the shear forecast to persist during until the waters cool and the atmosphere dries out, the intensity guidance has trended downward again this cycle, and so has the NHC prediction, which is close to or a little above HCCA and higher than the simple consensus aids. Karina should become a remnant low in about 4 days and is expected to dissipate by day 5. The initial motion estimate is 285/11. Karina should be steered generally west-northwestward for the next several days, followed by a turn toward the west in the low-level flow by 96 hours. The new NHC track forecast is similar to the previous one and lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 18.2N 117.1W 40 KT 45 MPH 12H 14/1200Z 18.7N 118.1W 40 KT 45 MPH 24H 15/0000Z 19.4N 119.7W 45 KT 50 MPH 36H 15/1200Z 20.2N 121.0W 45 KT 50 MPH 48H 16/0000Z 21.0N 122.1W 40 KT 45 MPH 60H 16/1200Z 21.8N 123.3W 35 KT 40 MPH 72H 17/0000Z 22.3N 124.5W 30 KT 35 MPH 96H 18/0000Z 22.5N 126.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 19/0000Z...DISSIPATED $$ Forecaster Brennan

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Tropical Depression Rene Forecast Discussion Number 28

2020-09-14 04:30:51| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 13 2020 000 WTNT43 KNHC 140230 TCDAT3 Tropical Depression Rene Discussion Number 28 NWS National Hurricane Center Miami FL AL182020 1100 PM AST Sun Sep 13 2020 Rene continues to produced puffs of deep convection that are continually being sheared away by nearly 30 kt of westerly shear. These brief convective bursts have not been sufficiently organized to warrant a Dvorak classification for about 12 hours, so if the convective organization does not increase soon, Rene could become a remnant low tonight. Continued shear and a very dry mid-level environment should result in Rene's remnants dissipating by 60 hours, if not sooner. Rene's forward speed has slowed since the last advisory, with a westward drift of 270/02 the current estimate. The shallow cyclone should accelerate west-southwestward or southwestward in the low-level flow by 24 hours and continue on that general motion until dissipation. The new NHC track forecast is adjusted south of the previous one toward the new multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 27.2N 47.9W 25 KT 30 MPH 12H 14/1200Z 27.3N 48.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 15/0000Z 26.9N 49.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 15/1200Z 26.2N 50.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 16/0000Z 25.5N 51.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 16/1200Z...DISSIPATED $$ Forecaster Brennan

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