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Tropical Storm ERIKA Forecast Discussion Number 10

2015-08-27 10:56:32| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU AUG 27 2015 000 WTNT45 KNHC 270856 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 AM AST THU AUG 27 2015 Data from a NOAA Hurricane Hunter aircraft indicate that Erika has strengthened overnight, although it is not clear as to how much. The central pressure dropped to around 1001 mb around 0540Z, but was up to 1003 mb on the next fix about an hour later. The highest 850-mb flight-level winds sampled by the aircraft were 48 kt, which would correspond to an intensity of around 40 kt. However, the aircraft found SFMR winds of 45 to 55 kt near the center. Based on a blend of these data, the initial intensity has been conservatively raised to 45 kt for this advisory. An Air Force Hurricane Hunter aircraft will be investigating Erika again later this morning. Aircraft data and satellite imagery show that Erika is still a sheared tropical cyclone, with the deepest convection found east and southeast of the center due to about 20 kt of westerly shear. The models show the environment remaining unfavorable for significant strengthening in the first 48 hours, with shear associated with an upper-level trough west of Erika expected to increase to 25 to 30 kt. Given this, most of the intensity guidance shows little change during the first couple of days and so does the NHC forecast. After that time, the upper trough weakens and Erika should encounter a more favorable upper-level pattern and warmer SSTs, which should support intensification assuming that the cyclone survives the next 48 hours. The HWRF and GFDL are much stronger than the statistical models this cycle, but the GFS and ECMWF now keep Erika weaker than they did previously. The NHC forecast has been adjusted upward slightly late in the period, but is well below the intensity consensus given the large uncertainty and spread in the guidance. Aircraft fixes and radar data from Guadeloupe were helpful in finding the low-level center and determining an initial motion of 280/14. The steering flow from the subtropical ridge to the north should result in a west-northwestward heading for the next 2 to 3 days. After that time, the spread in the guidance increases as the cyclone moves between the southwestern edge of the ridge and a mid/upper-level trough over the southeastern U.S. and Gulf of Mexico. The models are in poor agreement on the eventual structure and track of Erika late in the period. The ECMWF is weaker this cycle and is on the left side of the dynamical model envelope. The GFS, HWRF, and UKMET are all farther east but have trended west this cycle. Given the large spread and the continued run-to-run variability, little change was made to the NHC track forecast. The new NHC forecast is closest to the latest GFS model prediction at day 3 and beyond. One should remember to not focus on the exact forecast track, especially at the long range where the average NHC track errors during the past 5 years are about 180 miles at day 4 and 240 miles at day 5. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 16.8N 61.5W 45 KT 50 MPH 12H 27/1800Z 17.6N 63.5W 50 KT 60 MPH 24H 28/0600Z 19.0N 66.2W 50 KT 60 MPH 36H 28/1800Z 20.3N 69.0W 50 KT 60 MPH 48H 29/0600Z 21.5N 71.6W 50 KT 60 MPH 72H 30/0600Z 24.0N 76.0W 55 KT 65 MPH 96H 31/0600Z 26.5N 78.5W 65 KT 75 MPH 120H 01/0600Z 29.0N 79.5W 75 KT 85 MPH $$ Forecaster Brennan

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Tropical Storm JIMENA Forecast Discussion Number 3

2015-08-27 10:34:06| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU AUG 27 2015 000 WTPZ43 KNHC 270833 TCDEP3 TROPICAL STORM JIMENA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 200 AM PDT THU AUG 27 2015 The cyclone has become better organized on satellite pictures tonight, with a ball of convection near the center and some banding features. In addition, microwave data show a better defined low- level inner core structure. Dvorak satellite estimates from TAFB/SAB are both 35 kt and this will be the initial intensity. Microwave and night visible images give an initial motion of 285/13. The cyclone is expected to remain south of a deep-layer ridge located over northern Mexico and the eastern Pacific Ocean, and move generally westward along the southern periphery of the ridge for the next 3-4 days. By day 4, the western portion of the ridge is forecast to weaken some as a mid-latitude trough drops southward, steering Jimena on a west-northwestward track. Overall, the model guidance is just a bit faster by the end of the forecast period, and the NHC forecast follows that trend. There are no obvious impediments to intensification for Jimena during the next several days, with very warm water, moist mid-level air and little significant shear. The statistical and global models show a very powerful hurricane developing in a few days, and that solution seems likely given the large-scale environment. Thus, the official intensity forecast has been raised from the previous one, and the new NHC forecast is near or above the intensity consensus throughout most of the period. This forecast could be conservative with the LGEM and Florida State Superensemble showing an even stronger hurricane. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 12.3N 116.4W 35 KT 40 MPH 12H 27/1800Z 12.6N 118.3W 45 KT 50 MPH 24H 28/0600Z 13.0N 120.7W 60 KT 70 MPH 36H 28/1800Z 13.2N 123.0W 70 KT 80 MPH 48H 29/0600Z 13.1N 125.1W 80 KT 90 MPH 72H 30/0600Z 13.5N 128.8W 95 KT 110 MPH 96H 31/0600Z 15.0N 132.8W 110 KT 125 MPH 120H 01/0600Z 16.5N 137.0W 115 KT 130 MPH $$ Forecaster Blake

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Hurricane IGNACIO Forecast Discussion Number 9

2015-08-27 04:48:01| Tropical Depression LIDIA

Issued at 800 PM PDT WED AUG 26 2015

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Tropical Storm ERIKA Forecast Discussion Number 9

2015-08-27 04:45:03| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED AUG 26 2015 000 WTNT45 KNHC 270244 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 PM AST WED AUG 26 2015 Erika is a very disorganized tropical storm. Although convection has increased and is a little closer to the center tonight, data from both NOAA and Air Force reconnaissance plane indicate that the surface pressure is not falling, and the maximum winds remain about 40 kt. These winds are confined to squalls to the north and east of the center. Erika will be moving through a hostile wind shear environment as predicted by global models and the SHIPS guidance. On this basis, the NHC forecast weakens Erika to a 35-kt tropical storm and keeps that intensity for the next 48 hours. Erika, however, could even degenerate into a trough during the next day or so. If Erika survives the next 3 days and reaches the Bahamas, the environment is expected to become quite favorable. In fact, global models and the HWRF/GFDL pair forecast Erika to become a hurricane by the end of the forecast period. The NHC forecast is a little below the intensity consensus to reflect the possibility that the cyclone could dissipate before it reaches the Bahamas, and then it will be too late to take advantage of the more conducive environment there. Fixes from the reconnaissance planes indicate that Erika is moving toward the west or 280 degrees at 14 kt. The cyclone is embedded within well-established steering currents south of the Atlantic subtropical ridge. This persistent pattern will likely keep the cyclone or its remnants, in case it weakens, on a west to west-northwest motion for the next 3 days. After that time, the system will be in between the southwestern edge of the subtropical ridge and a mid-level trough, which is forecast to be nearly stationary along the east-central portion of the United States. This will force the cyclone to turn more to the northwest or even northward. Guidance shifted farther east tonight, and consequently, the NHC track forecast was adjusted slightly eastward, and it is very close to the consensus of the ECMWF and the GFS models. One should remember to not focus on the exact forecast track, especially at the long range where the average NHC track errors during the past 5 years are about 180 miles at day 4 and 240 miles at day 5. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 16.7N 60.2W 40 KT 45 MPH 12H 27/1200Z 17.4N 62.3W 35 KT 40 MPH 24H 28/0000Z 18.6N 65.0W 35 KT 40 MPH 36H 28/1200Z 20.0N 67.9W 35 KT 40 MPH 48H 29/0000Z 21.2N 70.5W 35 KT 40 MPH 72H 30/0000Z 23.5N 75.0W 45 KT 50 MPH 96H 31/0000Z 26.0N 78.3W 55 KT 65 MPH 120H 01/0000Z 28.5N 79.3W 65 KT 75 MPH $$ Forecaster Avila

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Tropical Storm ERIKA Forecast Discussion Number 8

2015-08-26 22:51:00| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED AUG 26 2015 000 WTNT45 KNHC 262050 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 PM AST WED AUG 26 2015 The satellite presentation of the tropical storm has become less organized since the previous advisory, with the low-level center becoming exposed to the northwest of the thunderstorm activity. A NOAA Hurricane Hunter aircraft investigating Erika this afternoon has not found flight-level or SFMR winds as strong as reported this morning, but the aircraft did not sample much of the eastern portion of the circulation. The initial intensity is held at 40 kt, but this could be generous. The intensity forecast philosophy has not changed since this morning. Erika is forecast to move through an area of moderate to strong westerly shear during the next two to three days. Although the NHC intensity forecast during that time shows no change in intensity, weakening is possible during the next couple of days. In fact, Erika could degenerate into a trough of low pressure due to the shear and interaction with the Greater Antilles. After 72 hours, the upper-level environment is forecast to become more conducive for development and all of the guidance, including the global models, shows intensification. Therefore, the days 4 and 5 intensity forecast again calls for strengthening, but is below the intensity consensus and near the SHIPS model. The official forecast leans toward the lower side of the guidance to reflect the possibility that the cyclone's structure would be too disrupted to fully take advantage of the more conducive environment late in the period. The initial motion remains 280/15 kt. Erika is forecast to move west-northwestward during the next three to four days to the south of a subtropical ridge over the western Atlantic. After that time, the global models show a weakness in the ridge developing over the far western Atlantic, which should cause Erika to turn northwestward. All of the models have shifted eastward at days four and five, but the normally reliable GFS and ECMWF define the western edge of the guidance. Out of respect of these models and the previous NHC forecast, the updated track has only been moved slightly eastward late in the period. As a result, the new forecast lies west of the multi-model consensus at 96 and 120 h. One should remember to not focus on the exact forecast track, especially at the long range where the average NHC track errors during the past 5 years are about 180 miles at day 4 and 240 miles at day 5. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.6N 58.9W 40 KT 45 MPH 12H 27/0600Z 17.1N 61.2W 40 KT 45 MPH 24H 27/1800Z 18.1N 64.0W 40 KT 45 MPH 36H 28/0600Z 19.2N 66.8W 40 KT 45 MPH 48H 28/1800Z 20.5N 69.6W 40 KT 45 MPH 72H 29/1800Z 22.7N 74.3W 40 KT 45 MPH 96H 30/1800Z 25.0N 77.7W 55 KT 65 MPH 120H 31/1800Z 27.5N 80.0W 65 KT 75 MPH $$ Forecaster Brown

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