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Hurricane Maria Forecast Discussion Number 17

2017-09-20 10:58:22| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 20 2017 000 WTNT45 KNHC 200858 TCDAT5 Hurricane Maria Discussion Number 17 NWS National Hurricane Center Miami FL AL152017 500 AM AST Wed Sep 20 2017 Radar observations from the San Juan WSR-88D and wind data from an Air Force Reserve Unit Hurricane Hunter aircraft indicate that Maria has just about completed an eyewall replacement. Based on the now-dominant outer eyewall, the eye diameter has increased from 10 n mi to 30 n mi. This has likely contributed to some weakening, and based on the latest observations from the Hurricane Hunters, the intensity is set at 135 kt which is at the top of category 4 range. Although there has been a slight reduction of intensity, Maria remains an extremely dangerous hurricane. Some weakening is likely while the system crosses Puerto Rico. Later in the forecast period, less favorable upper-level winds should cause further weakening, but Maria is likely to remain a large and powerful hurricane for the next 5 days. The official intensity forecast is near or a little above the model consensus. Maria continues to move between west-northwest and northwest at about 9 kt. The flow on the south side of a weak mid-level ridge over the western Atlantic is expected to steer the hurricane on this general heading over the next couple of days. This track will bring the center of Maria across Puerto Rico and just north of the eastern Dominican Republic over the next day or so. After that time a break in the ridge, partially associated with Tropical Storm Jose, should cause Maria to turn north-northwestward, then northward by the end of the forecast period. The track guidance remains tightly clustered through 72 hours, giving fairly high confidence in the track forecast through that time. There is some increase in the spread of the models at days 4 and 5, with the latest ECMWF prediction near the western edge of the guidance envelope but with all of the reliable models well offshore of the southeast U.S. at the end of the period. The official forecast is very close to the latest FSU Superensemble track. KEY MESSAGES: 1. Maria's core will make landfall over Puerto Rico within the next couple of hours, bringing life-threatening wind, storm surge, and rainfall impacts to the island. Everyone in Puerto Rico should follow advice from local officials to avoid life-threatening flooding from storm surge and rainfall. 2. Wind speeds atop and on the windward sides of hills and mountains and on high-rise buildings could be much stronger than the near-surface winds indicated in this advisory. 3. A Hurricane Warning is also in effect for the Virgin Islands, the northern coast of the Dominican Republic, the Turks and Caicos Islands and the southeastern Bahamas, where Maria is expected to bring dangerous wind, storm surge, and heavy rainfall. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 17.9N 65.6W 135 KT 155 MPH 12H 20/1800Z 18.6N 66.7W 125 KT 145 MPH...INLAND 24H 21/0600Z 19.5N 68.2W 120 KT 140 MPH 36H 21/1800Z 20.5N 69.4W 120 KT 140 MPH 48H 22/0600Z 21.5N 70.5W 115 KT 130 MPH 72H 23/0600Z 24.2N 72.0W 105 KT 120 MPH 96H 24/0600Z 27.3N 73.0W 100 KT 115 MPH 120H 25/0600Z 30.5N 73.0W 85 KT 100 MPH $$ Forecaster Pasch

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Tropical Storm Jose Forecast Discussion Number 60

2017-09-20 10:42:21| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Wed Sep 20 2017 000 WTNT42 KNHC 200842 TCDAT2 Tropical Storm Jose Discussion Number 60 NWS National Hurricane Center Miami FL AL122017 500 AM EDT Wed Sep 20 2017 Enhanced BD-curve infrared imagery shows considerable decay of yesterday afternoon's burst of deep convection near Jose's center. An earlier GPM low-frequency microwave overpass revealed that the strongest convection and associated winds were located in the north and west periphery of of the cyclone's circulation, a wind pattern indicative of non-tropical systems. Based on the deteriorating cloud pattern and a blend of the latest subjective T-numbers from TAFB and SAB, the initial intensity is lowered to 55 kt. Jose has begun its movement north of the Gulf Stream's north wall and over decreasing oceanic temperatures. Subsequent CIMSS shear analysis and the SHIPS model indicate modest southwesterly shear undercutting the outflow aloft. These inhibiting factors should result in additional weakening, and the official forecast calls for Jose to become a post-tropical cyclone in 48 hours, if not sooner. The initial motion is estimated to be northeastward, or 040/7 kt. There is no significant change to the previous track forecast or philosophy. The large-scale models continue to agree on Jose decreasing in forward speed and gradually turning toward the east on Thursday morning in response to a mid-tropospheric shortwave trough moving eastward out of the eastern Canadian provinces. Through the remainder of the forecast period, high pressure is expected to build over the northeast U.S. and adjacent waters, causing Jose to drift southward and southwestward through the 72 hour period. After that time, the cyclone is expected to basically meander in the northwest Atlantic within the weak steering flow produced by the aforementioned high pressure to the northwest of the cyclone and a building mid-level ridge to the southeast. The NHC forecast a little slower at days 4 and 5 and closely follows the GFS/ECMWF (GFEX) consensus and the forecast input from NOAA Ocean Prediction Center. KEY MESSAGES: 1. While the center of Jose is forecast to remain offshore of the U.S. east coast, the large cyclone is expected to cause some direct impacts in portions of New England, and a tropical storm warning is in effect for Cape Cod, Block Island, Martha's Vineyard, and Nantucket. 2. Minor to moderate coastal flooding is possible from Delaware to southern New England during the next several days. Please see products issued by local National Weather Service forecast offices. 3. Swells generated by Jose are affecting Bermuda, the Bahamas, and much of the U.S. east coast. These swells are likely to cause dangerous surf and rip current conditions for the next several days in these areas. 4. Jose is expected to produce additional rainfall accumulations of 1 to 2 inches over Martha's Vineyard and Cape Cod, and 2 to 4 inches in Nantucket as it passes offshore today into Thursday. This rainfall could cause isolated flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 38.4N 70.3W 55 KT 65 MPH 12H 20/1800Z 39.1N 69.3W 55 KT 65 MPH 24H 21/0600Z 39.6N 68.1W 50 KT 60 MPH 36H 21/1800Z 39.5N 67.8W 45 KT 50 MPH 48H 22/0600Z 39.2N 68.3W 40 KT 45 MPH...POST-TROPICAL 72H 23/0600Z 38.9N 69.4W 40 KT 45 MPH...POST-TROPICAL 96H 24/0600Z 39.2N 69.5W 35 KT 40 MPH...POST-TROPICAL 120H 25/0600Z 39.5N 68.9W 30 KT 35 MPH...POST-TROPICAL $$ Forecaster Roberts

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Tropical Storm Jose Forecast Discussion Number 59

2017-09-20 04:48:20| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Tue Sep 19 2017 000 WTNT42 KNHC 200248 TCDAT2 Tropical Storm Jose Discussion Number 59 NWS National Hurricane Center Miami FL AL122017 1100 PM EDT Tue Sep 19 2017 An Air Force plane once again investigated Jose tonight, and although the central pressure remained low, near 973 mb, the surface winds were gradually decreasing and do not support hurricane strength. This is also consistent with the latest Dvorak T-numbers which indicated weakening. On this basis, the initial intensity has been lowered to 60 kt. Although the shear is not too high, Jose is moving over cool waters. This should result in additional weakening and Jose is likely to become a post-tropical cyclone in about 48 hours. Fixes from a reconnaissance plane and satellite indicate that Jose is moving toward the northeast or 040 degrees at 8 kt. Currently, Jose in embedded within the mid-latitude southwesterly flow, but most of the global models forecast the development of a ridge to the north in two days. This new pattern should block the motion of the storm and Jose should begin to meander. The NHC forecast is very similar to the previous one and follows the ECMWF model and the HFIP corrected consensus model HCCA. It also uses the input from NOAA Ocean Prediction Center. KEY MESSAGES: 1. While the center of Jose is forecast to remain offshore of the U.S. east coast, the large cyclone is expected to cause some direct impacts in portions of New England, and a tropical storm warning is in effect for Cape Cod, Block Island, Martha's Vineyard, and Nantucket. Any deviation to the left of the NHC forecast track would increase the likelihood and magnitude of impacts along the coast from Long Island to southern New England. 2. Minor to moderate coastal flooding is possible from Delaware to southern New England during the next several days. Please see products issued by local National Weather Service forecast offices. 3. Swells generated by Jose are affecting Bermuda, the Bahamas, and much of the U.S. east coast. These swells are likely to cause dangerous surf and rip current conditions for the next several days in these areas. 4. Jose will produce total rainfall accumulations of 1 to 3 inches are expected over eastern Rhode Island and southeast Massachusetts. 2 to 4 inches are expected in Nantucket and Cape Cod, and 3 to 5 inches in Martha's Vineyard. This rainfall could cause isolated flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 37.9N 70.8W 60 KT 70 MPH 12H 20/1200Z 38.8N 69.9W 55 KT 65 MPH 24H 21/0000Z 39.6N 68.5W 50 KT 60 MPH 36H 21/1200Z 39.7N 67.7W 50 KT 60 MPH 48H 22/0000Z 39.5N 67.7W 45 KT 50 MPH...POST-TROPICAL 72H 23/0000Z 38.7N 69.0W 40 KT 45 MPH...POST-TROPICAL 96H 24/0000Z 38.5N 70.0W 35 KT 40 MPH...POST-TROPICAL 120H 25/0000Z 38.5N 70.5W 30 KT 35 MPH...POST-TROPICAL $$ Forecaster Avila

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Hurricane Maria Forecast Discussion Number 16

2017-09-20 04:45:21| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 19 2017 000 WTNT45 KNHC 200245 TCDAT5 Hurricane Maria Discussion Number 16 NWS National Hurricane Center Miami FL AL152017 1100 PM AST Tue Sep 19 2017 Since the previous advisory, WSR-88D radar data from San Juan Puerto Rico has shown the development of concentric eyewalls and a double-wind maximum. This has led to an increase in the size of the 50- and 64-kt wind radii. An earlier Air Force Reserve reconnaissance aircraft measured a peak flight-level wind of 157 kt and a few SFMR winds of 149-152 kt in the small inner eyewall between 2200 and 0000 UTC this evening. Based on these data, the initial wind speed was increased to 150 kt. The minimum pressure estimated from earlier dropsonde data is 909 mb, which is the tenth lowest minimum pressure recorded in an Atlantic basin hurricane. Since the outer eyewall has become better defined and the winds are increasing within the outer eyewall, it is likely that Maria's intensification will finally cease. However, Maria is expected to remain an extremely dangerous category 5 hurricane until landfall in Puerto Rico early Wednesday. The passage of the core over Puerto Rico should cause some weakening, but Maria is likely to remain a major hurricane for several more days. Increasing shear and cooler waters over the western Atlantic in the wake of hurricanes Irma and Jose will likely lead to additional weakening late in the period. Maria is moving between west-northwest and northwest at about 9 kt. A weak ridge over the western Atlantic is expected to steer the hurricane on this general heading over the next couple of days. This track will bring the center of Maria over Puerto Rico and just north of the eastern Dominican Republic over the next day or so. After that time, a break in the ridge should cause Maria to turn north-northwestward, then northward by late in the week. The track guidance is tightly clustered through 72 hours, yielding fairly high confidence in the track forecast through that time. There is some increase in the spread of the models at days 4 and 5, with the GFS and HWRF farther west and faster, while the ECMWF is along the eastern edge of the guidance and slow. For now, the NHC track forecast is between the various consensus models at 96 and 120 h. KEY MESSAGES: 1. Maria's core will pass near or over St. Croix within the next few hours and will approach the southeastern coast of Puerto Rico early Wednesday, bringing life-threatening wind, storm surge, and rainfall impacts to portions of those islands. Everyone in these areas should follow advice from local officials to avoid life-threatening flooding from storm surge and rainfall. 2. Wind speeds atop and on the windward sides of hills and mountains and on high-rise buildings could be much stronger than the near-surface winds indicated in this advisory. 3. A Hurricane Warning is also in effect for the remainder of the Virgin Islands and the northern coast of the Dominican Republic, where Maria is expected to bring dangerous wind, storm surge, and heavy rainfall. 4. A Hurricane Watch is in effect for the southeastern Bahamas and the Turks and Caicos, where Maria could bring hurricane conditions on Thursday. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 17.3N 64.7W 150 KT 175 MPH 12H 20/1200Z 18.0N 65.8W 145 KT 165 MPH 24H 21/0000Z 18.9N 67.3W 125 KT 145 MPH 36H 21/1200Z 19.9N 68.6W 120 KT 140 MPH 48H 22/0000Z 20.9N 69.7W 115 KT 130 MPH 72H 23/0000Z 23.3N 71.4W 110 KT 125 MPH 96H 24/0000Z 26.2N 72.2W 105 KT 120 MPH 120H 25/0000Z 29.5N 72.5W 90 KT 105 MPH $$ Forecaster Brown

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Post-Tropical Cyclone Norma Forecast Discussion Number 23

2017-09-20 04:32:55| Tropical Depression LIDIA

Issued at 800 PM PDT Tue Sep 19 2017

Tags: number discussion forecast norma

 

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