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Hurricane Dorian Forecast Discussion Number 30

2019-08-31 22:52:43| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sat Aug 31 2019 000 WTNT45 KNHC 312052 TCDAT5 Hurricane Dorian Discussion Number 30 NWS National Hurricane Center Miami FL AL052019 500 PM EDT Sat Aug 31 2019 Dorian's satellite presentation continues to be outstanding. The eye has remained very distinct and is surrounded by a ring of very deep convection. The latest information from the Air Force plane before it departed Dorian supports keeping an initial intensity of 130 kt. Dorian is forecast to move over a deep layer of very warm waters, and with the prevailing low shear along the hurricane's path, some additional strengthening is possible during the next day or so. Most likely, however, the hurricane will experience some fluctuations in intensity due to eyewall replacement cycles that are difficult to predict. Beyond 3 days, as the hurricane begins to gain latitude and encounters increasing shear, gradual weakening is anticipated, but Dorian will remain a dangerous hurricane through 5 days. The best estimate of the initial motion is toward the west or 280 degrees at 8 kt. The hurricane is being steered by the weak flow to the south of the ridge of high pressure over the western Atlantic. In about a day or two, most of the global models shift the high eastward and deepen a trough over the eastern United States. Consequently, the steering currents should collapse and Dorian is anticipated to drift toward the northwest and north-northwest while is moving over the northwestern Bahamas and near the east coast of Florida. After that time, the hurricane should begin to move a little faster northward as the trough over the eastern U.S deepens and should then steer the hurricane toward the northeast by the end of the forecast period. The guidance has not changed significantly since the earlier run, so it has not been necessary to adjust the NHC forecast in this advisory. The uncertainty in the track is high while the hurricane is moving slowly across the northwestern Bahamas and near the east coast of Florida. Any deviation of Dorian's core to the left would result in an increase in the winds along the east coast of Florida. Given that the area of tropical storm force winds could expand, and taking into account the uncertainty in the track forecast, a tropical storm watch was issued for the east of Florida from Deerfield Beach to Sebastian Inlet. Key Messages: 1. A prolonged period of life-threatening storm surge, devastating hurricane-force winds, and heavy rains capable of life-threatening flash floods are expected on the Abaco Islands and Grand Bahama Sunday through Monday, and a hurricane warning is in effect for these areas. 2. A tropical storm watch is in effect for a portion of the Florida east coast. Since Dorian is forecast to slow down and turn northward as it approaches the coast, life-threatening storm surge and dangerous hurricane-force winds are still possible along portions of the Florida east coast by the early to middle part of next week. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. There is an increasing risk of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina, and North Carolina during the middle of next week. Residents in these areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of life-threatening flash floods, are possible over coastal sections of the southeastern United States from Sunday through much of next week. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 26.2N 74.4W 130 KT 150 MPH 12H 01/0600Z 26.4N 75.7W 135 KT 155 MPH 24H 01/1800Z 26.6N 77.0W 130 KT 150 MPH 36H 02/0600Z 26.8N 78.0W 125 KT 145 MPH 48H 02/1800Z 27.2N 78.5W 120 KT 140 MPH 72H 03/1800Z 28.3N 79.1W 110 KT 125 MPH 96H 04/1800Z 31.0N 80.0W 95 KT 110 MPH 120H 05/1800Z 34.0N 77.0W 85 KT 100 MPH $$ Forecaster Avila/Brennan

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Hurricane Dorian Forecast Discussion Number 29

2019-08-31 16:56:08| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sat Aug 31 2019 000 WTNT45 KNHC 311456 TCDAT5 Hurricane Dorian Discussion Number 29 NWS National Hurricane Center Miami FL AL052019 1100 AM EDT Sat Aug 31 2019 Dorian's satellite presentation is outstanding with a distinct eye of about 15 n mi in diameter. Both NOAA and Air Force Hurricane Hunter planes have been penetrating the eye this morning and based on a blend of the flight-level and SFMR winds, the initial intensity has been adjusted upward to 130 kt in this advisory. Dorian is forecast to move over a deep layer of very warm waters, which is like high octane-fuel for hurricanes. The combination of the warm ocean and the prevailing low shear along Dorian's path should favor some additional strengthening, but most likely the hurricane will experience some fluctuations in intensity due to eyewall replacement cycles that are difficult to predict. Beyond 3 days, as the hurricane begins to gain in latitude a gradual weakening is anticipated. Plane fixes indicate that Dorian is moving toward the west or 280 degrees at 7 kt, steered by weak flow to the south of the ridge of high pressure over the western Atlantic. Most of the global models shift the high eastward and deepens a trough over the eastern United States beyond 2 days. This steering flow would typically favor a gradual turn of the hurricane to the northwest and north, however there is large uncertainty in the exact location and timing of this northward turn. Although the latest guidance has shifted a little bit eastward again this morning, there are still ECMWF and GFS ensemble members that do not forecast the northward turn so soon. On this basis, NHC prefers to shift the track forecast just a little bit to the right of the previous one, and the new official forecast lies along the western edge of the guidance envelope. This will allow for further adjustments in the track during future forecast cycles. Key Messages: 1. A prolonged period of life-threatening storm surge and devastating hurricane-force winds are expected in portions of the northwestern Bahamas, particularly on the Abaco Islands and Grand Bahama Island. A hurricane warning is in effect for these areas, and residents should listen to advice given by local emergency officials and have their hurricane preparations completed today. 2. Life-threatening storm surge and dangerous hurricane-force winds are still possible along portions of the Florida east coast by the early to middle part of next week, but since Dorian is forecast to slow down and turn northward near or just offshore of the coast, it is too soon to determine when or where the highest surge and winds could occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. The risk of strong winds and dangerous storm surge is increasing along the coasts of Georgia, South Carolina, and North Carolina during the middle of next week. Residents in these areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of life-threatening flash floods, are expected over portions of the Bahamas and coastal sections of the southeastern United States this weekend through much of next week. FORECAST POSITIONS AND MAX WINDS INIT 31/1500Z 26.0N 73.4W 130 KT 150 MPH 12H 01/0000Z 26.2N 74.7W 135 KT 155 MPH 24H 01/1200Z 26.6N 76.2W 130 KT 150 MPH 36H 02/0000Z 26.8N 77.4W 125 KT 145 MPH 48H 02/1200Z 27.0N 78.0W 120 KT 140 MPH 72H 03/1200Z 28.0N 79.0W 115 KT 130 MPH 96H 04/1200Z 30.5N 80.0W 100 KT 115 MPH 120H 05/1200Z 33.5N 78.0W 95 KT 110 MPH $$ Forecaster Avila

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Hurricane Dorian Forecast Discussion Number 28

2019-08-31 10:49:06| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Aug 31 2019 000 WTNT45 KNHC 310848 TCDAT5 Hurricane Dorian Discussion Number 28 NWS National Hurricane Center Miami FL AL052019 500 AM EDT Sat Aug 31 2019 Dorian continues to look impressive in satellite imagery this morning, with a fairly symmetric area of cold cloud tops surrounding a 10-15 n mi wide eye. There have been no new aircraft data from the storm since the last advisory. However, the satellite appearance has changed little since the aircraft were last in the storm, and the various subjective and objective satellite intensity estimates have changed little over the past several hours. Based on this, the initial intensity remains 120 kt. The initial motion is now 290/10. A low- to mid-level subtropical ridge to the north of the hurricane should steer it west- northwestward to westward for the next 48 h or so, with the forward speed becoming very slow as the center passes near or over the Abacos and Grand Bahama. The track guidance for this part of the track is tightly clustered, and the new forecast track is near the ECMWF, UKMET, and HCCA corrected consensus models. The track forecast becomes much more problematic after 48 h. The global models the NHC normally uses, along with the regional HWRF and HMON models, have made another shift to the east to the point where none of them forecast Dorian to make landfall in Florida. However, the UKMET ensemble mean still brings the hurricane over the Florida peninsula, as do several GFS and ECMWF ensemble members. The new track forecast for 72-120 h will be moved eastward to stay east of the coast of Florida, and it lies between the old forecast and the various consensus models. Additional adjustments to the forecast track may be necessary later today if current model trends continue. It should be noted that the new forecast track does not preclude Dorian making landfall on the Florida coast, as large portions of the coast remain in the track cone of uncertainty. Also, significant impacts could occur even if the center stays offshore. Dorian should remain in a generally favorable environment for the next 3-4 days, and the intensity guidance indicates it will remain a powerful hurricane during this time. The new intensity forecast calls for a little more strengthening today, then it shows a slow weakening that follows the trend of the intensity guidance. During this time, the biggest intensity changes may come from hard-to- forecast eyewall replacement cycles. Late in the forecast period, increased vertical shear and proximity to land is expected to cause some weakening. Key Messages: 1. A prolonged period of life-threatening storm surge and devastating hurricane-force winds are likely in portions of the northwestern Bahamas, particularly on the Abaco Islands and Grand Bahama Island. A hurricane warning is in effect for these areas, and residents should listen to advice given by local emergency officials and have their hurricane preparations completed today. 2. Life-threatening storm surge and devastating hurricane-force winds are still possible along portions of the Florida east coast by the early to middle part of next week, but since Dorian is forecast to slow down and turn northward near the coast, it is too soon to determine when or where the highest surge and winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. The risk of strong winds and life-threatening storm surge is increasing along the coasts of Georgia and South Carolina during the middle of next week. Residents in those areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of life-threatening flash floods, are expected over portions of the Bahamas and coastal sections of the southeastern United States this weekend through much of next week. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 25.8N 72.6W 120 KT 140 MPH 12H 31/1800Z 26.1N 74.0W 125 KT 145 MPH 24H 01/0600Z 26.5N 75.8W 125 KT 145 MPH 36H 01/1800Z 26.7N 77.2W 125 KT 145 MPH 48H 02/0600Z 26.9N 78.1W 120 KT 140 MPH 72H 03/0600Z 27.5N 79.4W 115 KT 130 MPH 96H 04/0600Z 29.5N 80.5W 110 KT 125 MPH 120H 05/0600Z 32.0N 80.5W 95 KT 110 MPH $$ Forecaster Beven

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Hurricane Dorian Forecast Discussion Number 27

2019-08-31 04:41:05| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Aug 30 2019 000 WTNT45 KNHC 310240 TCDAT5 Hurricane Dorian Discussion Number 27 NWS National Hurricane Center Miami FL AL052019 1100 PM EDT Fri Aug 30 2019 The cloud pattern of Dorian has become quite impressive in infrared satellite imagery this evening. The eye has become very distinct and is surrounded by a very symmetric ring of deep convection. The upper-level outflow has also improved. A NOAA Hurricane Hunter aircraft this evening has measured peak SFMR winds of 119 kt, and a dropsonde dropped in the northeastern eyewall had mean winds in the lowest 150 m that also supported winds of 118 kt, so the initial wind speed has been raised to 120 kt. The latest center drop indicates a minimum pressure of around 948 mb, down 22 mb since this afternoon. Since Dorian will be traversing SSTs of around 29C and remain in a low shear environment, the current intensification phase may not be over. The NHC forecast is above the guidance and calls for some additional strengthening in the short-term. After that, fluctuations in intensity are likely due to eyewall replacement cycles that are difficult to predict. Although some decrease in wind speed could occur when Dorian slows down and causes some upwelling, all indications are that Dorian will remain an extremely powerful hurricane for the next several days. The hurricane is moving west-northwestward or 300 degrees at 9 kt. The ridge to the north of Dorian is expected to build during the next 24 hours, and this should cause Dorian's heading to bend westward toward the northwestern Bahamas. After 48 hours, the global models show an erosion of the western portion of the ridge, which is expected to cause the steering currents to collapse and the hurricane to slow down considerably by day 3. Later in the period, the models have again trended to a more significant weakness in the ridge which allows Dorian to turn northwestward, then northward near the east coast of Florida. Although the deterministic versions of the global models have trended northeastward again, the GFS and UKMET ensemble means are farther to the left. The updated NHC track forecast has been nudged northeastward and lies between the multi-model consensus aids and the aforementioned ensemble means. Although the official forecast track has been nudged northeastward to near the east coast of Florida the risk of significant impacts over much of the Florida peninsula remains high. Key Messages: 1. A prolonged period of life-threatening storm surge and devastating hurricane-force winds are likely in portions of the northwestern Bahamas, where a hurricane warning is in effect. Residents should execute their hurricane plan and listen to advice given by local emergency officials. 2. Life-threatening storm surge and devastating hurricane-force winds are possible along portions of the Florida east coast by early next week, but since Dorian is forecast to slow down and turn northward near the coast, it is too soon to determine when or where the highest surge and winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. A prolonged period of storm surge, high winds, and rainfall is possible in portions of Florida into next week, including the possibility of hurricane-force winds over inland portions of the Florida peninsula. 4. Heavy rains, capable of life-threatening flash floods, are expected over portions of the Bahamas and coastal sections of the southeastern United States this weekend through much of next week. FORECAST POSITIONS AND MAX WINDS INIT 31/0300Z 25.5N 71.4W 120 KT 140 MPH 12H 31/1200Z 25.9N 72.8W 130 KT 150 MPH 24H 01/0000Z 26.3N 74.5W 130 KT 150 MPH 36H 01/1200Z 26.6N 76.0W 125 KT 145 MPH 48H 02/0000Z 26.8N 77.3W 125 KT 145 MPH 72H 03/0000Z 27.0N 78.6W 115 KT 130 MPH 96H 04/0000Z 28.3N 80.5W 110 KT 125 MPH 120H 05/0000Z 30.8N 81.2W 90 KT 105 MPH $$ Forecaster Brown

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Hurricane Dorian Forecast Discussion Number 26

2019-08-30 22:50:29| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Aug 30 2019 000 WTNT45 KNHC 302050 TCDAT5 Hurricane Dorian Discussion Number 26 NWS National Hurricane Center Miami FL AL052019 500 PM EDT Fri Aug 30 2019 High resolution satellite images show that Dorian's cloud pattern has become much better organized, with a distinct eye surrounded by a ring of very deep convection and fair upper-level outflow. Satellite intensity estimates, both objectivs from CIMMS and subjective from TAFB and SAB, are in good agreement with the 100-kt winds recently measured by a reconnaissance aircraft. This is the intensity assigned to Dorian in this advisory. Since the upper-level environment is already becoming more favorable for intensification and Dorian will be over high sea surface temperatures, the NHC forecast calls for additional intensification. Dorian is expected to be an extremely dangerous major hurricane as it moves through the northwestern Bahamas and near the east coast of the Florida peninsula in about 2 to 4 days. The ridge over the western Atlantic appears to be already building to the north of Dorian and is beginning to force the hurricane on a more west-northwest track or 300 degrees at 9 kt. The ridge is forecast to build even more and steer Dorian on a westward track for the next 3 to 4 days. However, the steering currents will then weaken, and this should result in a decrease in the hurricane's forward speed. Given the collapse of the steering currents, the track forecast by the end of the forecast period is highly uncertain, and any small deviation in the track could bring the core of the powerful hurricane well inland over the Florida, keep it near the coast, or offshore. The models have not been very consistent from run to run in terms of the timing of the northward turn, but there are more models now indicating that the turn could occur near the east coast of Florida instead of well inland. Given this latest change, the NHC forecast has been shifted just a little to the right at this time, but users should be prepared for additional adjustements to the left or right depending on future model trends. Based on the new forecast, a hurricane warning has been issued for poertions of the northwest Bahamas. However, given the slower forecast speed of Dorian, it is too soon to issue and watches for the Florida coast at this time. Key Messages: 1. Life-threatening storm surge and devastating hurricane-force winds are likely in portions of the northwestern Bahamas, where a hurricane warning is in effect. Residents should execute their hurricane plan and listen to advice given by local emergency officials. 2. Life-threatening storm surge and devastating hurricane-force winds are likely along portions of the Florida east coast by early next week, but since Dorian is forecast to slow down and turn northward near the coast, it is too soon to determine when or where the highest surge and winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. A prolonged period of storm surge, high winds and rainfall is possible in portions of Florida into next week, including the possibility of hurricane-force winds over inland portions of the Florida peninsula. 4. Heavy rains, capable of life-threatening flash floods, are expected over portions of the Bahamas and coastal sections of the southeastern United States this weekend through much of next week. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 25.0N 70.7W 100 KT 115 MPH 12H 31/0600Z 25.6N 72.0W 105 KT 120 MPH 24H 31/1800Z 26.2N 73.8W 110 KT 125 MPH 36H 01/0600Z 26.5N 75.4W 115 KT 130 MPH 48H 01/1800Z 26.8N 76.9W 120 KT 140 MPH 72H 02/1800Z 27.0N 78.8W 120 KT 140 MPH 96H 03/1800Z 27.5N 80.4W 120 KT 140 MPH...NEAR FL EAST COAST 120H 04/1800Z 30.0N 81.5W 85 KT 100 MPH...INLAND $$ Forecaster Avila

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