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Hurricane Irma Forecast Discussion Number 46

2017-09-10 16:50:11| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Sep 10 2017 000 WTNT41 KNHC 101450 TCDAT1 Hurricane Irma Discussion Number 46 NWS National Hurricane Center Miami FL AL112017 1100 AM EDT Sun Sep 10 2017 Latest observations from the Air Force Hurricane Hunters had flight-level winds that corresponded to surface winds near 110 kt. Thus, given sampling considerations, the 115-kt intensity is retained for this advisory. Irma should maintain this intensity until the center reaches the southwest Florida coast, and then begin to weaken while the system interacts with the landmass of the Florida peninsula. Increasing southwesterly shear associated with an upper-level trough should also cause weakening of the hurricane during the next day or so. More rapid weakening is likely after Irma moves into the southeastern United States in 24-36 hours, and the cyclone should weaken to a remnant low in 72 hours or sooner. The official intensity forecast is close to the simple and corrected consensus models. The center of Irma wobbled more northward over the past few hours and the initial motion estimate is about 350/8 kt. Irma is embedded within a broad mid-level gyre over the Gulf of Mexico. The cyclone is expected to be steered north-northwestward at a faster forward speed over the next day or two on the eastern side of the gyre. This will take Irma inland over northern Florida early on Monday and the southeastern United States over the next couple of days. The track guidance remains fairly tightly clustered with the ECMWF track a little to the left and slower than the other models. The official track forecast lies between the model consensus and the ECMWF solution. This is just slightly east of the previous official forecast. KEY MESSAGES: 1. Life-threatening wind and storm surge from Irma will continue in the Florida Keys and southwestern Florida today and spread into central and northwestern Florida tonight and Monday. Preparations in central and northwestern Florida should be rushed to completion. 2. There is imminent danger of life-threatening storm surge flooding along much of the Florida west coast, including the Florida Keys, where a Storm Surge Warning is in effect. The threat of catastrophic storm surge flooding is highest along the southwest coast of Florida, where 10 to 15 feet of inundation above ground level is expected. This is a life-threatening situation. 3. Irma will bring life-threatening wind impacts to much of Florida regardless of the exact track of the center. Wind hazards from Irma are also expected to spread northward through Georgia and into portions of Alabama, Tennessee, South Carolina, and North Carolina. 4. Irma is expected to produce very heavy rain and inland flooding across much of Florida and many other parts of the southeast United States. Rainfall occurring very quickly, at 2 to 4 inches per hour, will lead to flash flooding and rapid rises on creeks, streams, and rivers. Significant river flooding is likely over the next five days in the Florida peninsula and southeast Georgia, where average rainfall of 8 to 15 inches and isolated 20 inch amounts are expected. Significant river flooding is also possible beginning Monday and Tuesday in much of eastern and central Georgia, western South Carolina, and western North Carolina, where average rainfall of 3 to 8 inches and isolated 12 inch amounts are expected. Mountainous parts of these states will be especially vulnerable to flash flooding. Farther west, Irma is expected to produce average amounts of 2 to 5 inches in parts of Alabama and Tennessee, where isolated higher amounts and local flooding may occur. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 25.0N 81.5W 115 KT 130 MPH 12H 11/0000Z 26.6N 82.1W 110 KT 125 MPH 24H 11/1200Z 29.2N 83.0W 80 KT 90 MPH 36H 12/0000Z 31.9N 84.6W 40 KT 45 MPH...INLAND 48H 12/1200Z 33.8N 86.7W 30 KT 35 MPH...INLAND 72H 13/1200Z 36.0N 89.0W 25 KT 30 MPH...POST-TROP/INLAND 96H 14/1200Z 38.5N 86.5W 20 KT 25 MPH...POST-TROP/INLAND 120H 15/1200Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Irma Forecast Discussion Number 45

2017-09-10 11:01:09| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Sep 10 2017 000 WTNT41 KNHC 100901 TCDAT1 Hurricane Irma Discussion Number 45 NWS National Hurricane Center Miami FL AL112017 500 AM EDT Sun Sep 10 2017 An Air Force Reserve Hurricane Hunter aircraft reported 700-mb flight-level winds of 128 kt in the northeastern eyewall, along with surface wind estimates of 110-115 kt from the Stepped Frequency Microwave Radiometer. In addition, the aircraft data shows that the central pressure has fallen to 928 mb. Based on these data, the initial intensity has been increased to 115 kt, again making Irma a Category 4 hurricane. Irma has made its long-awaited turn, with the initial motion now 325/7. For the next 36-48 h, the cyclone will be steered generally north-northwestward with an increase in forward speed between a low- to mid-level ridge over the western Atlantic and a developing mid- to upper-level low over the Gulf Coast states and the northern Gulf of Mexico. After that, the system should turn northwestward and then move somewhat erratically near the end of its life as it merges with the low. The tightly-clustered track guidance has changed little since the last advisory, and the new NHC forecast is very close to the previous one. The eye should move across the Lower Florida Keys in the next few hours. After that, the hurricane's track almost parallel to the west coast of Florida makes it very difficult to pinpoint exactly where Irma will cross the Florida Gulf coast. Given current trends, some additional strengthening could occur during the next several hours. However, vertical wind shear is increasing over Irma, and the shear is expected to become strong within 24 h. This, combined with land interaction, should cause at least a steady weakening from 12-36 h. The new intensity forecast is slightly lower than that of the previous advisory at those times, but it still calls for Irma to be a major hurricane at its closest approach to the Tampa Bay area. A faster weakening is likely after Irma moves across the Florida Panhandle and starts to merge with the aforementioned upper-level low, and the new forecast follows the trend of the previous one in calling for the system to decay to a remnant low by 72 h and to dissipate completely by 120 h. KEY MESSAGES: 1. Irma is expected bring life-threatening wind and storm surge to the Florida Keys and southwestern Florida as an extremely dangerous major hurricane today, and these conditions will spread into central and northwestern Florida tonight and Monday. Preparations in the Florida Keys and southwest Florida should be complete since hurricane-force winds are spreading into that area. 2. There is an imminent danger of life-threatening storm surge flooding along much of the Florida west coast, including the Florida Keys, where a Storm Surge Warning is in effect. The threat of catastrophic storm surge flooding is highest along the southwest coast of Florida, where 10 to 15 feet of inundation above ground level is expected. This is a life-threatening situation. 3. Irma will bring life-threatening wind impacts to much of Florida regardless of the exact track of the center. Wind hazards from Irma are also expected to spread northward through much of Georgia and portions of South Carolina and Alabama. 4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 15 to 20 inches with isolated amounts of 25 inches are expected over the Florida Keys through Sunday evening. Through Monday, Irma is expected to produce rainfall amounts of 8 to 15 inches with isolated amounts of 20 inches across the Florida peninsula and southeast Georgia, while across the rest of Georgia, eastern Florida Panhandle, southern and western South Carolina, and western North Carolina, a total of 3 to 6 inches with isolated amounts of 10 inches are expected. Significant river flooding is possible in these areas. Through Tuesday, Irma will also bring periods of heavy rain into the Tennessee Valley, where an average of 2 to 5 inches with isolated higher amounts is forecast across eastern Alabama and southern Tennessee. This includes some mountainous areas which are more prone to flash flooding. Residents throughout the southeast states should remain aware of the flood threat and stay tuned to forecasts and warnings. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 24.1N 81.5W 115 KT 130 MPH 12H 10/1800Z 25.4N 82.0W 115 KT 130 MPH 24H 11/0600Z 27.8N 82.8W 100 KT 115 MPH 36H 11/1800Z 30.5N 84.1W 75 KT 85 MPH...INLAND 48H 12/0600Z 32.7N 85.8W 40 KT 45 MPH...INLAND 72H 13/0600Z 35.5N 89.0W 25 KT 30 MPH...POST-TROP/INLAND 96H 14/0600Z 37.5N 88.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 15/0600Z...DISSIPATED $$ Forecaster Beven

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Hurricane Jose Forecast Discussion Number 20

2017-09-10 10:58:17| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 10 2017 000 WTNT42 KNHC 100858 TCDAT2 Hurricane Jose Discussion Number 20 NWS National Hurricane Center Miami FL AL122017 Issued by the NWS Weather Prediction Center College Park MD 500 AM AST Sun Sep 10 2017 Jose remains a category four hurricane on the Saffir-Simpson Hurricane Wind Scale, with a 15 n mi wide eye continuing to be surrounded a solid ring of deep convection. Little significant change in the overall satellite appearance has been observed since a Hurricane Hunter plane sampled the cyclone earlier in the night, and the initial intensity remains unchanged at 115 kt. The initial motion is 310/14 kt, with Jose's track through the first 24 hours being driven by a mid-level ridge located to the north-northeast of the cyclone. After this time, the steering pattern is expected to become rather dynamic, leading to a 5-day forecast that shows Jose making a small anticyclonic loop over the open waters of the western Atlantic. This occurs as the ridge shifts to the east of Jose from 36 to 48 hours, leading to a reduction in forward speed, and a gradual turn toward the north. A turn toward the east and southeast is expected on days 3 and 4, with an even slower forward motion, as the ridge weakens and moves south of the system. Late in the forecast period, the ridge is expected to build to the northwest and then north of Jose, leading to a gradual acceleration toward the west, and a reduction in the shear. With such a complex steering pattern expected, it comes as no surprise that the track guidance diverges significantly in the latter forecast periods. The updated forecast is close to the previous one, lies close to the FSSE, and is in between the GFS and ECMWF, which are more than 250 miles apart on day 5. The shear over Jose is currently analyzed to be near 10 kt, but north to northeasterly shear is forecast to increase in the short term and remain relatively strong through 48 hours due to Jose moving closer to a building ridge to its northwest. This will lead to a weakening trend, despite the system remaining over SSTs near 29 Celsius. The official intensity forecast is nudged down ever so slightly from the previous one through day 3, but remains higher than the SHIPS model, due to the ECMWF and GFS models maintaining a more intense system. The intensity prediction on days 4 and 5 remains unchanged due to forecast environmental uncertainties at that time. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 20.8N 64.5W 115 KT 130 MPH 12H 10/1800Z 22.2N 66.1W 110 KT 125 MPH 24H 11/0600Z 24.2N 67.9W 105 KT 120 MPH 36H 11/1800Z 25.6N 69.0W 100 KT 115 MPH 48H 12/0600Z 26.5N 68.8W 95 KT 110 MPH 72H 13/0600Z 26.3N 67.0W 90 KT 105 MPH 96H 14/0600Z 25.0N 66.5W 90 KT 105 MPH 120H 15/0600Z 24.5N 70.0W 90 KT 105 MPH $$ Forecaster Birchard/Blake

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Hurricane Jose Forecast Discussion Number 19

2017-09-10 04:58:15| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 09 2017 000 WTNT42 KNHC 100258 TCDAT2 Hurricane Jose Discussion Number 19 NWS National Hurricane Center Miami FL AL122017 Issued by the NWS Weather Prediction Center College Park MD 1100 PM AST Sat Sep 09 2017 Jose continues to have an impressive satellite signature, with a nearly clear 15 to 20 n mi wide eye surrounded by a ring of deep convection. An Air Force Hurricane Hunter plane just finished a mission through Jose, with maximum flight-level winds of 122 kt and maximum SFMR winds of 109 kt. Based on this data, the initial intensity for this advisory is estimated to be 115 kt. The initial motion remains a steady 310/12 kt, with Jose's motion through the first 36 hours being driven by a deep-layer ridge located to the north of the cyclone. As the ridge shifts to the east of the system on day 2, a turn toward the north is expected, with a decrease in the forward motion. By day 3, the steering currents are expected to become quite weak, with Jose moving north of the mid-level ridge, while a deep-layer low passes well to the northeast. This will induce a short-lived motion to the east, but as the ridge rebuilds west and then north of Jose, a gradual westward turn of the cyclone is expected. The 5-day forecast depicts Jose completing a relatively small anticyclonic loop over the open Atlantic. The updated forecast is close to the previous one, and closely follows the consensus guidance and operational ECMWF/GFS/UKMET. The shear over Jose is currently analyzed to be near 10 kt, and thus little change in short-term intensity is expected. Although water temperatures will be sufficiently warm to support an intense cyclone, moderate shear - of varying directions - is expected to lead to gradual weakening over the next couple of days as Jose meanders over the open Atlantic. The updated intensity forecast is close to the previous prediction, but is stronger than the SHIPS model, due to the IVCN/ECMWF models maintaining a more intense system. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 19.8N 63.4W 115 KT 130 MPH 12H 10/1200Z 21.1N 65.1W 115 KT 130 MPH 24H 11/0000Z 22.8N 67.2W 110 KT 125 MPH 36H 11/1200Z 24.4N 68.8W 105 KT 120 MPH 48H 12/0000Z 25.5N 69.3W 100 KT 115 MPH 72H 13/0000Z 26.3N 68.0W 95 KT 110 MPH 96H 14/0000Z 25.2N 67.3W 90 KT 105 MPH 120H 15/0000Z 24.5N 69.0W 90 KT 105 MPH $$ Forecaster Birchard/Blake

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Hurricane Irma Forecast Discussion Number 44

2017-09-10 04:58:08| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Sep 09 2017 000 WTNT41 KNHC 100258 TCDAT1 Hurricane Irma Discussion Number 44 NWS National Hurricane Center Miami FL AL112017 1100 PM EDT Sat Sep 09 2017 Irma's nearly 24-hour traversal of the north coast of Cuba appears to have affected the hurricane's structure and intensity. An earlier NOAA Hurricane Hunter aircraft and a more recent Air Force reconnaissance flight both measured maximum flight-level winds near 105 kt and surface winds near 95 kt. The planes have reported a double eyewall structure, which has also been observed in WSR-88D Doppler radar data from Miami and Key West. Irma's intensity has been conservatively lowered to 105 kt, and I'd rather wait to lower the winds further until we've seen the full data set from the Air Force mission. Irma has stuttered near the north coast of Cuba for the past few hours, which may be a harbinger of the north-northwestward turn that we've been waiting for. In any event, Irma appears to be moving very slowly toward the northwest, or 305/5 kt, very gradually shifting away from the north coast of Cuba. With the hurricane located near a break in the subtropical ridge, it should turn north-northwestward soon and accelerate near or along the west coast of Florida during the next 36-48 hours. Because of Irma's hesitation to move northwestward, the new track guidance has shifted ever so slightly westward, and the new NHC track is just a little left of the previous one. Although it is likely that the eye will move near or over the Lower Keys Sunday morning, the hurricane's angle of approach to the west coast of Florida makes it very difficult to pinpoint exactly where Irma will cross the Florida Gulf coast. If an eyewall replacement occurs within the next 6-12 hours, Irma has an opportunity to restrengthen a bit while it moves across the Straits of Florida. After that time, however, southwesterly shear is expected to increase to 25-30 kt in about 24 hours and then continue increasing through 48 hours. This shear, in addition to Irma's core interacting with Florida, is likely to cause a weakening trend after 24 hours. The new intensity guidance calls for an adjustment from the previous forecast, although it conservatively lies near the upper bound of the reliable models. Irma is still expected to approach the Florida Keys and Florida west coast as a major hurricane, and combined with its large size, will produce significant storm surge flooding in those areas. KEY MESSAGES: 1. Irma is expected bring life-threatening wind and storm surge to the Florida Keys and southwestern Florida as an extremely dangerous major hurricane tonight through Sunday. Preparations in the Florida Keys and southwest Florida should be complete since tropical-storm- force winds are already affecting portions of the coast. 2. There is an imminent danger of life-threatening storm surge flooding in portions of central and southern Florida, including the Florida Keys, where a Storm Surge Warning is in effect. The threat of catastrophic storm surge flooding is highest along the southwest coast of Florida, where 10 to 15 feet of inundation above ground level is expected. This is a life-threatening situation, and everyone in these areas should immediately follow any evacuation instructions from local officials. 3. Irma will bring life-threatening wind impacts to much of Florida regardless of the exact track of the center. Wind hazards from Irma are also expected to spread northward through much of Georgia and portions of South Carolina and Alabama. 4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 10 to 20 inches, with isolated amounts of between 20 and 25 inches, are expected over the Florida Keys, the Florida peninsula, and southeast Georgia from Saturday through Monday. Significant river flooding is possible in these areas. Early next week Irma will also bring periods of heavy rain to much of the southeast United States where an average of 2 to 6 inches is forecast, with isolated higher amounts, from North and South Carolina to Tennessee and eastern Alabama. This includes some mountainous areas which are more prone to flash flooding. Residents throughout the southeast states should remain aware of the flood threat and stay tuned to forecasts and warnings. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 23.5N 81.0W 105 KT 120 MPH 12H 10/1200Z 24.7N 81.7W 110 KT 125 MPH 24H 11/0000Z 26.8N 82.4W 105 KT 120 MPH 36H 11/1200Z 29.5N 83.4W 80 KT 90 MPH...ON THE COAST 48H 12/0000Z 32.2N 85.0W 55 KT 65 MPH...INLAND 72H 13/0000Z 35.3N 89.0W 25 KT 30 MPH...POST-TROP/INLAND 96H 14/0000Z 37.0N 88.5W 20 KT 25 MPH...POST-TROP/INLAND 120H 15/0000Z...DISSIPATED $$ Forecaster Berg

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