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Hurricane Irma Forecast Discussion Number 36

2017-09-08 05:00:27| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Thu Sep 07 2017 000 WTNT41 KNHC 080300 TCDAT1 Hurricane Irma Discussion Number 36 NWS National Hurricane Center Miami FL AL112017 1100 PM EDT Thu Sep 07 2017 Microwave images and data from an Air Force Reserve Hurricane Hunter aircraft indicate that Irma is developing a concentric eyewall structure, and the plane reported an elliptical eye. The highest flight-level and SFMR winds measured by the aircraft were 146 kt and 139 kt, respectively, so the initial intensity is lowered slightly to 145 kt. Irma's central pressure has fallen a bit despite the slight reduction in winds, counterbalanced by an expansion of the hurricane-force wind field as observed by the plane. If Irma has developed concentric eyewalls, then some additional gradual weakening or fluctuations in intensity are possible over the next day or two, despite a seemingly favorable atmospheric and oceanic environment. The intensity models depict a very gradual decrease in Irma's maximum winds up until a possible landfall in Florida, but the hurricane is nonetheless expected to still be at or near category 4 strength at that time. After landfall, a fairly quick decay in maximum winds is expected due to land interaction and increased shear, although Irma's large wind field is likely to still produce hurricane-force winds over a large area. Irma continues to move west-northwestward at 290/14 kt, steered by the western extent of the subtropical ridge. Irma should maintain this trajectory but slow down during the next 36 hours, and then turn north-northwestward toward a break in the ridge by 72 hours. Although there was a westward shift in the 18Z GFS, this model's new track puts it very close to the previous NHC forecast. As such, no major changes to the NHC track were required on this forecast through 72 hours, and the projected path lies between the GFS and ECMWF, closest to the TVCN consensus and HCCA. After 72 hours, the models are showing a more pronounced turn toward the northwest when Irma interacts with a shortwave diving southeastward from the Central Plains, and the NHC forecast has been adjusted accordingly at the end of the forecast period. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will continue to bring life-threatening wind, storm surge, and rainfall hazards to the Turks and Caicos Islands and the Bahamas through Saturday. Heavy rainfall is still possible across portions of Hispaniola through Friday. Hurricane conditions will also spread over portions of the north coast of Cuba, especially over the adjacent Cuban Keys through Saturday. 2. Severe hurricane conditions are expected over portions of the Florida peninsula and the Florida Keys beginning late Saturday. Irma could make landfall in southern Florida as a dangerous major hurricane, and bring life-threatening storm surge and wind impacts to much of the state. A Hurricane Warning is in effect for southern Florida, the Florida Keys, Lake Okeechobee, and Florida Bay, while Hurricane Watches have been issued northward into central Florida. 3. A Storm Surge Warning is in effect for southern Florida and the Florida Keys. A Storm Surge Warning means there is a danger of life-threatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a life-threatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials. A Storm Surge Watch has been issued north of the Storm Surge Warning for portions of the central Florida coast. 4. There is a chance of direct impacts in portions of Georgia, South Carolina, and North Carolina, but it is too early to specify the magnitude and location of these impacts. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 21.3N 72.4W 145 KT 165 MPH 12H 08/1200Z 21.8N 74.4W 145 KT 165 MPH 24H 09/0000Z 22.3N 76.7W 140 KT 160 MPH 36H 09/1200Z 22.9N 78.6W 135 KT 155 MPH 48H 10/0000Z 23.7N 79.9W 135 KT 155 MPH 72H 11/0000Z 27.2N 81.1W 100 KT 115 MPH...INLAND 96H 12/0000Z 32.0N 83.5W 50 KT 60 MPH...INLAND 120H 13/0000Z 35.5N 86.5W 30 KT 35 MPH...INLAND $$ Forecaster Berg

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Hurricane Katia Forecast Discussion Number 10

2017-09-08 04:53:24| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Thu Sep 07 2017 000 WTNT43 KNHC 080253 TCDAT3 Hurricane Katia Discussion Number 10 NWS National Hurricane Center Miami FL AL132017 1000 PM CDT Thu Sep 07 2017 The Air Force Hurricane Hunters have been investigating Katia this evening and found flight level winds of 80 kt and SFMR values around 75 kt. Based on these data, the initial wind speed is nudged upward to 75 kt. Satellite images also show that Katia is getting better organized, with a ragged eye becoming apparent during the last hour or so. Additional strengthening is possible, and Katia could be near major hurricane strength before it makes landfall by Saturday morning. After landfall, rapid weakening is expected, and Katia is forecast to dissipate over the rugged terrain of the Sierra Madre mountains shortly after 48 hours. Katia has now begun the expected slow west-southwest motion. A continued slow west-southwestward motion is expected until the system dissipates. The NHC track forecast is similar to the previous one and near the consensus models. In addition to the hurricane-force winds, very heavy rains associated with Katia is forecast to affect eastern Mexico. These rains could cause life-threatening flash floods and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 21.5N 95.1W 75 KT 85 MPH 12H 08/1200Z 21.3N 95.5W 85 KT 100 MPH 24H 09/0000Z 20.8N 96.4W 90 KT 105 MPH 36H 09/1200Z 19.9N 97.5W 55 KT 65 MPH...INLAND 48H 10/0000Z 19.3N 98.3W 25 KT 30 MPH...INLAND 72H 11/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Jose Forecast Discussion Number 11

2017-09-08 04:49:25| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Sep 07 2017 000 WTNT42 KNHC 080249 TCDAT2 Hurricane Jose Discussion Number 11 NWS National Hurricane Center Miami FL AL122017 1100 PM AST Thu Sep 07 2017 After strengthening quickly throughout the day, the intensity of Jose appears to have leveled off this evening. Nonetheless, Jose is an impressive category 3 hurricane. The eye remains quite distinct and the convective cloud pattern is fairly symmetric. In addition, the upper-level outflow is well established, indicative of the favorable wind flow pattern aloft. The initial intensity is held at 105 kt, in accordance with the Dvorak CI numbers from TAFB and SAB. Some slight strengthening is possible during the next 12 to 24 hours while Jose remains in relatively conducive environmental conditions. Thereafter, a slow weakening trend is forecast due to an increase in wind shear and a progressively drier air mass. The models are in fair agreement, and the NHC official intensity forecast is in line with the consensus models. This forecast is slightly lower than the previous one. The initial motion is 280/16 kt. The track forecast philosophy is unchanged from earlier. A subtropical ridge should cause Jose to move west-northwestward for the next couple of days, taking the hurricane very near the northern Leeward Islands Friday night and Saturday. After that time, the hurricane is expected to move northwestward and then northward into a weakness in the ridge. The NHC track forecast is largely an update of the previous one and near the middle of the guidance envelope. Based on the latest forecast, the government of Antigua has issued a tropical storm warning for Antigua, Barbuda, and Anguilla. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 15.6N 53.9W 105 KT 120 MPH 12H 08/1200Z 16.1N 56.1W 110 KT 125 MPH 24H 09/0000Z 16.8N 58.5W 110 KT 125 MPH 36H 09/1200Z 17.8N 60.5W 105 KT 120 MPH 48H 10/0000Z 19.2N 62.2W 100 KT 115 MPH 72H 11/0000Z 22.6N 66.1W 90 KT 105 MPH 96H 12/0000Z 25.8N 68.2W 75 KT 85 MPH 120H 13/0000Z 27.1N 67.4W 70 KT 80 MPH $$ Forecaster Cangialosi

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Hurricane Irma Forecast Discussion Number 35

2017-09-07 22:59:52| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Thu Sep 07 2017 000 WTNT41 KNHC 072059 TCDAT1 Hurricane Irma Discussion Number 35 NWS National Hurricane Center Miami FL AL112017 500 PM EDT Thu Sep 07 2017 Hurricane Irma continues to have an impressive satellite presentation with a very distinct eye. There is not much more to add about the current intensity except that numerous data from the Air Force reconnaissance plane indicate that the winds remain at 150 kt. The environment along the future track of Irma is favorable for the hurricane to maintain most of its current intensity, although some fluctuations are likely due to eyewall replacement cycles which are difficult to predict. There are no obvious reasons why Irma should not remain a powerful major hurricane for the next 3 days while it is heading for Florida or its adjacent surroundings. Thereafter, an increase in the wind shear and the interaction with land should lead to gradual weakening. The best estimate of the initial motion is toward the west-northwest or 285 degrees at 14 kt. Irma is being steered by the flow around the south side of the subtropical ridge, but in 2 or 3 days the hurricane is expected to be located on the southwestern edge of the aforementioned ridge, and a turn to the northwest and north- northwest should then begin. The forecast track for the first 2 days was adjusted a little bit to the south given that the ridge to the north continues to be strong, and the ECMWF and HFIP corrected consensus (HCCA) models have shifted southward a little bit. These two models have been performing very well during Irma. This adjustment also results in a westward shift of the track near Florida and northward. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will continue to bring life-threatening wind, storm surge, and rainfall hazards to the northern coast of Hispaniola tonight. These hazards are already spreading across the Turks and Caicos and will affect the Bahamas tonight through Saturday. Hurricane conditions will also spread over portions of the north coast of Cuba, especially over the adjacent Cuban Keys through Saturday. 2. It has become more likely that Irma will make landfall in southern Florida as a dangerous major hurricane, and bring life-threatening storm surge and wind impacts to much of the state. A Hurricane Watch is in effect for South Florida, the Florida Keys, Lake Okeechobee, and Florida Bay, and will likely be expanded northward tonight. 3. A Storm Surge Watch is in effect for portions of South Florida and the Florida Keys. This means there is the possibility of life-threatening inundation from rising water moving inland from the coastline during the next 48 hours in these areas. The Potential Storm Surge Flooding Map depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded. Because the Flooding Map is based on inputs that extend through 72 hours, it best represents the flooding potential in the watch area. 4. There is a chance of direct impacts in portions of Georgia, South Carolina, and North Carolina, but it is too early to specify the magnitude and location of these impacts. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 20.9N 71.1W 150 KT 175 MPH 12H 08/0600Z 21.6N 73.1W 145 KT 165 MPH 24H 08/1800Z 22.2N 75.5W 140 KT 160 MPH 36H 09/0600Z 22.7N 77.6W 135 KT 155 MPH 48H 09/1800Z 23.4N 79.3W 135 KT 155 MPH 72H 10/1800Z 26.2N 80.7W 115 KT 130 MPH...INLAND 96H 11/1800Z 31.5N 82.0W 80 KT 90 MPH...INLAND 120H 12/1800Z 36.0N 84.0W 40 KT 45 MPH...INLAND $$ Forecaster Avila

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Hurricane Jose Forecast Discussion Number 10

2017-09-07 22:34:40| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 07 2017 000 WTNT42 KNHC 072034 TCDAT2 Hurricane Jose Discussion Number 10 NWS National Hurricane Center Miami FL AL122017 Issued by the NWS Weather Prediction Center College Park MD 500 PM AST Thu Sep 07 2017 Jose has continued to develop a well-defined eye on satellite imagery this afternoon, with the eye now established in the center of a ring of strong convection. 18 UTC Dvorak fixes from TAFB and SAB came in at T5.5, which suggests 100 knot intensity. However, given the ongoing improvements in satellite presentation and CIMSS ADT numbers which have since climbed higher, the initial intensity for this advisory is set at 105 knots. This makes Jose a Category 3 hurricane on the Saffir-Simpson Hurricane Wind Scale. It is the third major hurricane in the 2017 Atlantic hurricane season (Harvey, Irma). It also means we have two major hurricanes simultaneously in the Atlantic basin, which is not too common -- especially in such close proximity. The last time this happened was in 2010 when Igor and Julia were both major hurricanes on September 15-16, and then Igor and Karl were both major hurricanes briefly on September 17. In the near-term, most factors appear aligned for continued intensification. Outflow remains well-established in all quadrants, and Jose has thus far not felt negative impacts from the dry air situated just to its west and northwest. For this reason, we are taking the intensity up to 120 knots at the 24 hour forecast point. After that, a gradual decrease in intensity is shown, in line with most intensity guidance. However, the intensity forecast generally lies above most of the guidance in deference to the ongoing rapid intensification trend. Global models do show that some of the dry air to the west of Jose may wrap into the circulation in about 24-36 hours. That may be a contributing factor to the decrease in intensity, as well as some increasing shear at the base of an upper level low in the central Atlantic and perhaps the periphery of Irma's upper level outflow. The smaller size of Jose may make it a little more vulnerable to effects of dry air and shear. The initial motion remains at 285/16kt, and Jose will continue to be steered by a well established subtropical ridge. It should not reach the ridge axis until about 36-48 hours, at which point the ridge begins to erode a bit and Jose may turn a bit more toward the northwest and eventually the north. The forecast track remains very similar to the previous official forecast through 48 hours -- roughly between the operational GFS and ECMWF and close to the multi-model consensus. After that time, the steering flow becomes weaker and the forward motion should slow down. Models begin to diverge more significantly at 96hr and especially 120hr. The forecast at these time ranges lies closer to the multi-model consensus and the operational ECMWF than models that show a quicker exit to the east. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 15.5N 52.4W 105 KT 120 MPH 12H 08/0600Z 16.0N 54.8W 115 KT 130 MPH 24H 08/1800Z 16.6N 57.6W 120 KT 140 MPH 36H 09/0600Z 17.3N 59.8W 110 KT 125 MPH 48H 09/1800Z 18.4N 61.7W 105 KT 120 MPH 72H 10/1800Z 21.9N 65.5W 95 KT 110 MPH 96H 11/1800Z 25.5N 67.9W 80 KT 90 MPH 120H 12/1800Z 27.3N 67.2W 75 KT 85 MPH $$ Forecaster Lamers/Carbin

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