Home › discussion
 

Keywords :   


Tag: discussion

Hurricane Florence Forecast Discussion Number 56

2018-09-13 10:56:17| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Thu Sep 13 2018 440 WTNT41 KNHC 130856 TCDAT1 Hurricane Florence Discussion Number 56 NWS National Hurricane Center Miami FL AL062018 500 AM EDT Thu Sep 13 2018 The satellite presentation of Florence has changed little overnight with the eye waxing and waning in infrared imagery. The eye has moved into NWS radar range and can be seen in radar data from Morehead City and Wilmington NWS 88-D imagery. An 0616 UTC AMSR2 microwave overpass indicated that the convection over the southern and southeastern portions of the storm is still disrupted, and that the eyewall was open to the southeast. An Air Force Hurricane Hunter aircraft also reported that the eyewall was not fully intact on its last pass through the storm just after that time. The Air Force plane measured a peak 700-mb flight level wind of 102 kt and peak SFMR winds of 85 kt during the mission. These data suggest that the intensity may be slightly lower, but the initial intensity has been maintained at 95 kt, since the plane may not have sampled the strongest winds. Another Air Force plane will be in Florence shortly, and should provide a better assessment of the intensity of the hurricane. As mentioned in the previous discussion, it appears that some southern shear has caused the degradation of the inner core. The global models suggest that this shear will relax today while Florence moves over warm waters, however, given the current storm structure, little overall change in strength is anticipated as Florence approaches the coast. Gradual weakening should occur as the hurricane interacts with land in 24-36 h, with a faster rate of weakening predicted once Florence moves farther inland. Florence is moving northwestward or 315 degrees at 13 kt. A developing mid-level ridge over the north-central United States should cause the forward speed of the hurricane to decrease today. As the steering currents collapse tonight and Friday, Florence is forecast to drift westward or west-southwestward and continue that slow motion into the weekend. The global models predict that the ridge will slide eastward over the weekend, which should allow Florence to turn northwestward and northward by the end of the forecast period. Although there is still some spread in the guidance by 48 hours, with the GFS along the northern side of the guidance envelope, and the ECWMF along the southern edge, the various consensus aids have moved little. As a result, the new NHC forecast track is very similar to the previous advisory. Aircraft and satellite wind data show that Florence is a large hurricane. Life-threatening storm surge, heavy rainfall, and damaging wind will cover a large area regardless of exactly where the center of Florence moves. Key Messages: 1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area. All interests in these areas should complete preparations and follow any advice given by local officials. 2. Life-threatening, catastrophic flash flooding and prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians late this week into early next week, as Florence is expected to slow down as it approaches the coast and moves inland. 3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 32.8N 74.7W 95 KT 110 MPH 12H 13/1800Z 33.7N 76.1W 95 KT 110 MPH 24H 14/0600Z 34.2N 77.4W 90 KT 105 MPH 36H 14/1800Z 34.3N 78.4W 70 KT 80 MPH...INLAND 48H 15/0600Z 34.1N 79.2W 50 KT 60 MPH...INLAND 72H 16/0600Z 33.9N 81.2W 30 KT 35 MPH...INLAND 96H 17/0600Z 35.4N 83.3W 25 KT 30 MPH...INLAND 120H 18/0600Z 39.5N 81.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

Tags: number discussion forecast florence

 

Hurricane Helene Forecast Discussion Number 24

2018-09-13 10:48:17| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 13 2018 082 WTNT43 KNHC 130848 TCDAT3 Hurricane Helene Discussion Number 24 NWS National Hurricane Center Miami FL AL082018 500 AM AST Thu Sep 13 2018 Helene's surface circulation has become fully exposed this morning with the center decoupled about 110 miles south of edge of the remaining deep convection. Subjective and objective satellite intensity estimates have decreased and support lowering the initial intensity to 65 kt. Statistical and global model guidance show the southwesterly shear increasing significantly in 12 hours or so, however, the 26 to 27C sea surface temperatures should govern the weakening trend a little. In 3 days, Helene is forecast to move over much cooler waters while the cyclone becomes embedded in the hostile mid-latitude upper-level westerlies. Subsequently, further weakening is expected at a faster pace. By day 4, the large-scale models all show Helene acquiring extratropical cyclone characteristics as it moves toward Ireland and the United Kingdom. The NHC intensity forecast is similar to the previous advisory, and is based primarily on the NOAA-HCCA and the IVCN consensus models. Helene is still moving northward, or 355/12 kt, within the deep-layer southerly flow produced by an amplifying mid-Atlantic trough to the west of the cyclone. In 48 hours, Helene is forecast to turn north-northeastward followed by a turn toward the northeast with an increase in forward motion at the 72 hour period. The guidance suite remains tightly clustered through day 4, with some slight spread at day 5, and indicates that Helene will pass near the Azores in about 3 days. Interests in those islands should closely monitor the progress of Helene over the next few days. The official forecast is basically an update of the previous one, and lies close to the TVCN multi-model consensus through the entire forecast period. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 23.5N 37.3W 65 KT 75 MPH 12H 13/1800Z 25.7N 37.4W 60 KT 70 MPH 24H 14/0600Z 29.1N 36.9W 55 KT 65 MPH 36H 14/1800Z 32.5N 36.2W 55 KT 65 MPH 48H 15/0600Z 35.8N 34.7W 55 KT 65 MPH 72H 16/0600Z 40.7N 28.2W 50 KT 60 MPH 96H 17/0600Z 44.6N 19.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0600Z 51.1N 10.8W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts

Tags: number discussion forecast hurricane

 
 

Tropical Storm Isaac Forecast Discussion Number 22

2018-09-13 04:53:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 12 2018 907 WTNT44 KNHC 130253 TCDAT4 Tropical Storm Isaac Discussion Number 22 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Wed Sep 12 2018 A NOAA P-3 Hurricane Hunter plane has been investigating Isaac this evening, and the data show that the cyclone has weakened a bit. The maximum 850-mb flight-level wind measured by the plane was 47 kt, and the highest SFMR winds not coincident with a rain spike were around 45 kt. Based on these wind data, the initial intensity is lowered to 45 kt, and the minimum pressure is up to 1006 mb based on dropsonde data. Additionally, a superposition of the flight-level wind and dropsonde surface wind data suggest that Isaac may not have a closed circulation at 850 mb but is still hanging on to one at the surface. All of Isaac's deep convection is displaced 60-120 n mi to the northeast and southeast of the low-level center due to around 30 kt of westerly shear. This magnitude of the shear is not expected to decrease during the next 12-24 hours, so at the very least, gradual weakening is anticipated. With the circulation so fragile and limited to below 850 mb, however, it's entirely possible that Isaac could open up into a wave at any time. Even if degeneration into a wave occurs, the system would likely carry tropical-storm-force winds across the Leeward Islands on Thursday. After Isaac moves into the eastern Caribbean Sea, there is a lot of uncertainty regarding its future. The 18Z GFS has come back in line with the ECMWF, showing Isaac opening up into a trough over the central and western Caribbean Sea, but the environmental conditions (lower shear, warm sea surface temperatures, etc.) would suggest that the system would have an opportunity to restrengthen. For now, the new NHC intensity forecast maintains continuity from the previous advisory, showing gradual weakening through 48 hours and then holding the system at 35 kt through day 5. This remains a low confidence forecast until we know if Isaac survives the next couple of days. Isaac continues to move quickly westward with an initial motion of 270/17 kt. The track guidance remains tightly clustered on a nearly due westward motion for much of the forecast period, with some of the same speed differences noted in previous forecasts. Especially since Isaac's speed has been faster than forecast, the NHC track forecast continues to favor the faster guidance, in particular the ECMWF, GFS, and HCCA models. Reconnaissance and scatterometer data suggest that there are no tropical-storm-force winds within the southern semicircle, but the radii we've been carrying within the northern semicircle appear reasonable. The wind radii forecast have been adjusted to account for the new initial radii. Key Messages: 1. Isaac is expected to still be producing tropical-storm-force winds when it moves across the Lesser Antilles on Thursday, and tropical storm warnings are in effect for Martinique, Dominica, and Guadeloupe. Tropical storm watches are in effect for Montserrat, St. Kitts and Nevis, Antigua, Saba and St. Eustatius, St. Maarten, and St. Martin. Interests on those islands should follow any advice given by their local officials. 2. Life-threatening flash flooding is possible with Isaac. The storm is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up 8 inches across Martinique, Dominica and Guadeloupe. Rainfall amounts of 1 to 2 inches with isolated amounts to 4 inches are expected across Puerto Rico and the southern United States Virgin Islands. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 15.3N 58.0W 45 KT 50 MPH 12H 13/1200Z 15.5N 60.4W 45 KT 50 MPH 24H 14/0000Z 15.6N 63.4W 40 KT 45 MPH 36H 14/1200Z 15.7N 66.4W 40 KT 45 MPH 48H 15/0000Z 15.7N 69.2W 35 KT 40 MPH 72H 16/0000Z 15.6N 73.9W 35 KT 40 MPH 96H 17/0000Z 16.5N 77.5W 35 KT 40 MPH 120H 18/0000Z 17.5N 82.0W 35 KT 40 MPH $$ Forecaster Berg

Tags: number discussion storm tropical

 

Hurricane Florence Forecast Discussion Number 55

2018-09-13 04:49:14| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Wed Sep 12 2018 874 WTNT41 KNHC 130249 TCDAT1 Hurricane Florence Discussion Number 55 NWS National Hurricane Center Miami FL AL062018 1100 PM EDT Wed Sep 12 2018 Satellite data and reports from Hurricane Hunter aircraft indicate significant changes in the structure of Florence and the environment near the storm since the last advisory. Microwave satellite imagery shows that the convection on the southern side of the storm has been disrupted, and reports from an Air Force Reserve Hurricane Hunter aircraft indicate the eyewall now wraps less than 50 percent of the way around the center. The aircraft also reports that the hurricane again has concentric wind maxima, the inner at a radius 20-30 n mi and the outer at 50-60 n mi. The convection seems to have been affected by 20-25 kt of southerly vertical wind shear, most of which appears to be due to strong winds between 200-250 mb seen in dropsonde data from the NOAA G-IV jet. The central pressure has risen to 957 mb, and the maximum 700-mb flight-level winds reported so far are 103 kt. Based on the latter data, the initial intensity reduced to a probably generous 95 kt. The initial motion is 315/15. During the next 12-36 hours, the hurricane is expected to turn toward the west-northwest and west with a decrease in forward speed as it moves into an area of weakening steering currents near and over the southeastern United States. The new forecast track now brings the center onshore in southern North Carolina near the 36 h point. After landfall, the cyclone should move slowly westward to west-southwestward through the 72 h point, then it should turn northwestward to northward by the end of the forecast period as it moves through the Appalachian Mountains. The new forecast track lies between the HCCA corrected consensus model and the other consensus aids, and it is nudged just a little to the north of the previous track. The dynamical models forecast the current shear to subside after 6-12 h as Florence moves farther from an upper-level low currently near northeastern Florida. This, combined with sea surface temperatures near 29C, would allow a last chance for strengthening before landfall. However, the storm structure, particularly the large outer wind maxima, would likely be slow to respond to the more favorable environment. The pre-landfall part of the intensity forecast thus calls for little change in strength, but given the uncertainties the confidence in this is low. After landfall, Florence should gradually weaken during the 36-48 h period while the center is near the coast, then weaken more quickly when the center moves farther inland. While Florence has weakened below major hurricane intensity, the wind field of the hurricane continues to grow in size. This evolution will produce storm surges similar to that of a more intense, but smaller, hurricane, and thus the storm surge values seen in the previous advisory are still valid. The threat of rainfall has also not diminished, and these impacts will cover a large area regardless of exactly where the center of Florence moves. Key Messages: 1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area. All interests in these areas should complete preparations and follow any advice given by local officials. 2. Life-threatening, catastrophic flash flooding and prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians late this week into early next week, as Florence is expected to slow down as it approaches the coast and moves inland. 3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 32.0N 73.7W 95 KT 110 MPH 12H 13/1200Z 33.1N 75.3W 95 KT 110 MPH 24H 14/0000Z 33.9N 76.7W 95 KT 110 MPH 36H 14/1200Z 34.2N 78.0W 80 KT 90 MPH...INLAND 48H 15/0000Z 34.1N 78.7W 60 KT 70 MPH...INLAND 72H 16/0000Z 33.5N 80.5W 40 KT 45 MPH...INLAND 96H 17/0000Z 34.0N 83.0W 25 KT 30 MPH...INLAND 120H 18/0000Z 37.5N 83.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

Tags: number discussion forecast florence

 

Subtropical Storm Joyce Forecast Discussion Number 2

2018-09-13 04:45:15| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 12 2018 610 WTNT45 KNHC 130245 TCDAT5 Subtropical Storm Joyce Discussion Number 2 NWS National Hurricane Center Miami FL AL102018 1100 PM AST Wed Sep 12 2018 Joyce still has subtropical characteristics. Although a small area of convection has recent developed near the storm's center, cloud tops are not particularly cold and the cyclone is still co-located with an upper-level low. The initial intensity has been held at 40 kt based on a subtropical intensity estimate of 35-40 kt from TAFB. This could be generous estimate since a recent near-miss of the ASCAT instrument to the west of Joyce suggested that the winds may have decreased somewhat since earlier today. Little change has been made to the track or intensity forecast. Just about all of the intensity guidance continues to indicate that some gradual strengthening is possible during the next day or two while Joyce continues to acquire tropical characteristics. By 72 h, the global and statistical models depict Joyce weakening due to a drastic increase in shear and a decrease in environmental humidity until it is absorbed into a larger mid-latitude trough around 96 h. The HWRF and HMON models show a very different solution where Joyce strengthens to hurricane strength despite the marginal environment. This scenario seems less likely at this time, so the NHC intensity forecast is just below the intensity consensus beyond 36 h. Joyce is caught in fairly light steering currents between strong ridges to its east and west, and the initial motion estimate is 220/5 kt. All of the global models forecast only a slow southwestward motion during the next couple of days, particularly as Hurricane Helene approaches from the southeast. Once Helene passes to the east, Joyce will likely quickly turn northeastward and accelerate ahead of the aforementioned mid-latitude trough before dissipating southwest of the Azores. The official track forecast is basically a blend of the previous advisory and the corrected consensus aids HCCA and FSSE. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 34.1N 42.6W 40 KT 45 MPH 12H 13/1200Z 33.5N 43.3W 40 KT 45 MPH 24H 14/0000Z 32.9N 43.8W 45 KT 50 MPH...TROPICAL STORM 36H 14/1200Z 32.5N 44.0W 50 KT 60 MPH 48H 15/0000Z 32.3N 43.4W 50 KT 60 MPH 72H 16/0000Z 34.2N 40.0W 45 KT 50 MPH 96H 17/0000Z 37.0N 33.5W 40 KT 45 MPH 120H 18/0000Z...DISSIPATED $$ Forecaster Zelinsky

Tags: number discussion storm forecast

 

Sites : [506] [507] [508] [509] [510] [511] [512] [513] [514] [515] [516] [517] [518] [519] [520] [521] [522] [523] [524] [525] next »