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Hurricane Irma Forecast Discussion Number 41
2017-09-09 11:06:09| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Sat Sep 09 2017 000 WTNT41 KNHC 090905 TCDAT1 Hurricane Irma Discussion Number 41 NWS National Hurricane Center Miami FL AL112017 500 AM EDT Sat Sep 09 2017 The eye of Irma has been moving over the islands along the north coast of Cuba, and satellite imagery along with preliminary data from an Air Force Reserve Hurricane Hunter aircraft indicates that the hurricane has weakened. The initial intensity is reduced to 135 kt, and this may be generous. The initial motion is now 285/10. Irma is moving along the southwestern side of the subtropical ridge, which is about to weaken due to a mid- to upper-level trough moving into the southeastern United States. The track guidance is in good agreement that Irma should continue west-northwestward for the next 12-24 h, followed by a turn toward the north-northwest that would take the center parallel to the west coast of the Florida peninsula. Later in the forecast period, the cyclone should turn northwestward and eventually stall as it interacts with the aforementioned trough. The track guidance has changed only slightly since the previous advisory. Thus the new forecast track follows the previous forecast in calling for Irma to move along the coast of Cuba, then over the Lower Florida Keys, and then over and near the Florida West coast. It should be noted that because of the hurricane's angle of approach to the west coast of Florida, it is extremely difficult to pinpoint exactly where the center might move onshore. There is an opportunity for Irma to re-intensity as it crosses the warm waters of the Florida Straits. However, the large-scale models forecast significant westerly shear developing at about 24 h, and it is unclear how much strengthening could occur before then. The first part of the intensity forecast thus calls for little change in strength through 36 h, and Irma is still expected to be a dangerous hurricane as it approaches the Florida Keys and the west coast of Florida. After that time, movement over land and strong shear should cause steady weakening, with Irma eventually decaying to a remnant low by the end of the forecast period. KEY MESSAGES: 1. Irma will continue to bring life-threatening wind, storm surge, and rainfall hazards to portions of the Bahamas and the north coast of Cuba, especially over the adjacent Cuban Keys, through tonight. 2. Irma is expected to make landfall in Florida as an extremely dangerous major hurricane, and will bring life-threatening wind impacts to much of the state regardless of the exact track of the center. 3. There is the danger of life-threatening storm surge inundation in portions of central and southern Florida, including the Florida Keys, during the next 36 hours, where a Storm Surge Warning is in effect. The threat of significant storm surge flooding along the southwest coast of Florida has increased, and 8 to 12 feet of inundation above ground level is possible in this area. This is a life-threatening situation. Everyone in these areas should take all actions to protect life and property from rising water and follow evacuation instructions from local officials. 4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 8 to 15 inches, with isolated amounts of 20 inches are expected over the Florida Keys and much of the Florida peninsula through Tuesday night. Irma will likely bring periods of heavy rain to much of the Florida Panhandle, Georgia, South Carolina, and western North Carolina early next week, including some mountainous areas which are more prone to flash flooding. All areas seeing heavy rainfall from Irma will experience a risk of flooding and flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 22.5N 78.8W 135 KT 155 MPH 12H 09/1800Z 22.9N 80.0W 130 KT 150 MPH 24H 10/0600Z 23.8N 81.1W 130 KT 150 MPH 36H 10/1800Z 25.4N 81.8W 130 KT 150 MPH 48H 11/0600Z 27.7N 82.4W 105 KT 120 MPH...INLAND 72H 12/0600Z 32.5N 84.5W 45 KT 50 MPH...INLAND 96H 13/0600Z 35.5N 88.0W 25 KT 30 MPH...INLAND 120H 14/0600Z 36.0N 87.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Beven
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Hurricane Jose Forecast Discussion Number 16
2017-09-09 10:54:02| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 09 2017 000 WTNT42 KNHC 090853 TCDAT2 Hurricane Jose Discussion Number 16 NWS National Hurricane Center Miami FL AL122017 500 AM AST Sat Sep 09 2017 There has been some weakening of the inner core this morning, specifically, considerable warming of the cloud tops and partial erosion of the western portion of the eyewall. Indications from earlier microwave passes and radar imagery from the Leeward Island of Guadeloupe reveal the possibility of an ongoing eyewall replacement cycle (ERC). Subsequently, the initial intensity is generously lowered to 130 kt for this advisory. An aircraft reconnaissance mission later this morning will provide a more accurate measure of Jose's intensity. Whether or not Jose completes the ERC cycle during the next several hours is uncertain. Regardless of the inner core structural transition, Jose is still forecast to be a category 4 hurricane as it closely approaches the northern Leeward Islands today. Statistical and dynamical intensity guidance show gradual weakening of the cyclone through day 5 as a result of increasing northerly shear and drier, more stable mid-tropospheric air associated with an approaching mid-latitude trough to the northwest of the cyclone. The official forecast is above all of the available guidance through 24 hours, then corresponds to the IVCN multi-model consensus. The initial motion is estimated to be west-northwestward, or 300/11 kt. The eye of Jose is expected to turn northwestward and pass just east of the northern Leeward Islands later today. Jose should slow down and turn north-northwestward in 72 hours in response to the aforementioned deep-layer mid-level trough. Large-scale models have come in alignment with the trough leaving Jose behind to meander in weaker mid-level westerly flow through day 5. The NHC forecast is basically an update of the previous package and is based on a blend of the HFIP Corrected Consensus model and the ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 17.5N 60.3W 130 KT 150 MPH 12H 09/1800Z 18.4N 61.8W 125 KT 145 MPH 24H 10/0600Z 19.9N 63.9W 115 KT 130 MPH 36H 10/1800Z 21.5N 65.9W 110 KT 125 MPH 48H 11/0600Z 23.1N 67.6W 100 KT 115 MPH 72H 12/0600Z 25.7N 69.0W 90 KT 105 MPH 96H 13/0600Z 26.5N 67.6W 80 KT 90 MPH 120H 14/0600Z 26.4N 66.3W 80 KT 90 MPH $$ Forecaster Roberts
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Tropical Storm Katia Forecast Discussion Number 15
2017-09-09 10:34:15| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sat Sep 09 2017 000 WTNT43 KNHC 090834 TCDAT3 Tropical Storm Katia Discussion Number 15 NWS National Hurricane Center Miami FL AL132017 Issued by the NWS Weather Prediction Center College Park MD 400 AM CDT Sat Sep 09 2017 Convection has substantially diminished with Katia, with satellite imagery showing a significantly degraded structure. In fact, it seems that the low-level circulation may be decoupled from the low center aloft now, as a distinct circulation in diminishing colder cloud tops moved more quickly off to the southwest. There was already evidence of this occurring from the recon flight earlier tonight. The initial position was determined via the circulation in warmer clouds in the lower troposphere on IR satellite. Katia is very close to the higher terrain of the Sierra Madre Mountains, and thus the forecast shows very little movement this morning as the increasingly shallow circulation would be less likely to propagate west through the mountainous areas. The initial intensity is set at 35 knots out of respect for the hurricane strength Dvorak fixes only nine hours ago, and the extent of tropical storm force winds sampled by the recon plane shortly thereafter, although this could be generous. The most likely location of tropical storm force winds would be away from the center and over the water or near the coast in the eastern semicircle of Katia's circulation. The wind field should continue to weaken this morning, and we show a dissipation of Katia by 18Z today. Although convection has generally diminished as of 09Z, lingering elevated levels of atmospheric moisture associated with Katia could continue to produce heavy rains in the region, which could lead to flash floods and mudslides even after Katia dissipates. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 20.3N 97.5W 35 KT 40 MPH 12H 09/1800Z 20.2N 97.6W 20 KT 25 MPH...INLAND 24H 10/0600Z...DISSIPATED $$ Forecaster Lamers/Roth
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Hurricane Irma Forecast Discussion Number 40
2017-09-09 05:00:03| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Sep 08 2017 000 WTNT41 KNHC 090259 TCDAT1 Hurricane Irma Discussion Number 40 NWS National Hurricane Center Miami FL AL112017 1100 PM EDT Fri Sep 08 2017 An Air Force Hurricane Hunter flight has found that Irma has re-intensified to category 5 strength. The plane measured a maximum flight-level wind of 154 kt and SFMR winds of 140-145 kt in the northwestern eyewall, so the initial intensity is raised to 140 kt. The hurricane is producing very deep convection in all quadrants around the eye, which the Air Force flight measured to be 35 n mi wide. Apparently the ridge to the north of Irma has been stronger than expected, and the initial motion remains westward, or 280/11 kt. The track guidance continues to insist on Irma turning west-northwestward soon, moving along the Cuban Keys adjacent to the north coast of Cuba during the next 24 hours. After that time, Irma is expected to turn sharply north-northwestward and accelerate after 48 hours, moving parallel to the west coast of Florida and then into Georgia. Mainly because Irma's eye has not deviated from its westward motion, the new NHC forecast track has again shifted slightly westward. Because of the hurricane's angle of approach to the west coast of Florida, it is extremely difficult to pinpoint exactly where the center might move onshore. If the eye continues to move over the Cuban Keys and does not move inland over the main island of Cuba, then Irma would likely not lose much intensity during the next day or so. As we've stated many times, fluctuations in intensity are likely during the next 36 hours due to possible and unpredictable eyewall replacement cycles. After 36 hours, there are some indications that vertical shear may increase over the hurricane, and a little more weakening is anticipated at that time. Because of the concerns in the track forecast noted above, Irma would be able to maintain a strong intensity for a longer period of time if the center stays off the west Florida coast. Regardless, Irma is still expected to be a dangerous hurricane as it approaches the Florida Keys and the west coast of Florida through 48 hours. KEY MESSAGES: 1. Irma will continue to bring life-threatening wind, storm surge, and rainfall hazards to portions of the Bahamas and the north coast of Cuba, especially over the adjacent Cuban Keys, through Saturday. 2. Irma is expected to make landfall in Florida as an extremely dangerous major hurricane, and will bring life-threatening wind impacts to much of the state regardless of the exact track of the center. 3. There is the danger of life-threatening storm surge inundation in portions of central and southern Florida, including the Florida Keys, during the next 36 hours, where a Storm Surge Warning is in effect. The threat of significant storm surge flooding along the southwest coast of Florida has increased, and 8 to 12 feet of inundation above ground level is possible in this area. This is a life-threatening situation. Everyone in these areas should take all actions to protect life and property from rising water and follow evacuation instructions from local officials. 4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 8 to 15 inches, with isolated amounts of 20 inches are expected over the Florida Keys and much of the Florida peninsula through Tuesday night. Irma will likely bring periods of heavy rain to much of the Florida Panhandle, Georgia, South Carolina, and western North Carolina early next week, including some mountainous areas which are more prone to flash flooding. All areas seeing heavy rainfall from Irma will experience a risk of flooding and flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 22.1N 77.7W 140 KT 160 MPH 12H 09/1200Z 22.6N 79.1W 140 KT 160 MPH 24H 10/0000Z 23.3N 80.6W 135 KT 155 MPH 36H 10/1200Z 24.5N 81.4W 130 KT 150 MPH 48H 11/0000Z 26.5N 81.9W 115 KT 130 MPH...INLAND 72H 12/0000Z 31.6N 83.8W 50 KT 60 MPH...INLAND 96H 13/0000Z 35.0N 87.0W 25 KT 30 MPH...INLAND 120H 14/0000Z 35.5N 87.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Berg
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Hurricane Jose Forecast Discussion Number 15
2017-09-09 04:42:59| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 08 2017 000 WTNT42 KNHC 090242 TCDAT2 Hurricane Jose Discussion Number 15 NWS National Hurricane Center Miami FL AL122017 1100 PM AST Fri Sep 08 2017 The Air Force Hurricane Hunters have been investigating Jose this evening and found that the hurricane is even a little stronger than previously estimated. An average of the aircraft's flight level winds, SFMR values, and dropsonde data support an intensity of 135 kt, making Jose very near category 5 strength. It is surprising that Jose is as strong as the aircraft data suggests, since the hurricane's satellite appearance has degraded a little during the last several hours. Jose is moving west-northwestward at 12 kt. A west-northwest to northwest motion is expected overnight and on Saturday, taking the core of Jose just east of the northern Leeward Islands. The hurricane is forecast to slow down and turn northward in 3 to 4 days when it moves around the ridge and toward a large mid- to upper-level low over the north Atlantic. The models then indicate that the upper low will bypass Jose causing it to drift eastward or meander at the end of the forecast period. The track forecast is fairly close to the previous advisory and lies nearest to the various consensus models. Fluctuations in strength are likely overnight and on Saturday due to the potential for eyewall replacement cycles, but Jose is expected to remain at category 4 strength when it is closest to the northern Leeward Islands. After that time, the models insist that a slow weakening trend should occur through the remainder of the forecast period due to an increase in wind shear and drier air. The NHC intensity forecast lies at the high end of the guidance in the short term, but then falls in line with the HCCA and ICON consensus models from 48 to 120 h. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 16.9N 59.3W 135 KT 155 MPH 12H 09/1200Z 17.8N 60.8W 130 KT 150 MPH 24H 10/0000Z 19.1N 62.8W 120 KT 140 MPH 36H 10/1200Z 20.7N 64.8W 115 KT 130 MPH 48H 11/0000Z 22.4N 66.8W 105 KT 120 MPH 72H 12/0000Z 25.3N 68.8W 95 KT 110 MPH 96H 13/0000Z 26.8N 68.0W 90 KT 105 MPH 120H 14/0000Z 27.7N 66.3W 80 KT 90 MPH $$ Forecaster Cangialosi
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