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Tropical Storm Irma Forecast Discussion Number 51

2017-09-11 22:36:51| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Mon Sep 11 2017 000 WTNT41 KNHC 112036 TCDAT1 Tropical Storm Irma Discussion Number 51 NWS National Hurricane Center Miami FL AL112017 500 PM EDT Mon Sep 11 2017 Surface synoptic data over the southeastern United States indicate that Irma continues to weaken. The maximum winds are now near 45 kt, and these are confined to the Georgia and South Carolina coastal area, along with some winds to tropical storm force in interior central to northern Georgia. Irma continues to have some extratropical characteristics, since a fairly well-defined baroclinic zone lies not far from the center. Nevertheless, the large circulation should continue to spin down due to land interaction and strong southwesterly shear. The official intensity forecast is above most of the guidance, so the system could weaken faster than shown here. Irma should weaken to a depression in 24 hours or sooner, and the global guidance shows the circulation dissipating over the east-central United States after 48 hours. Synoptic center fixes give a continued north-northwestward motion of 340/15 kt. There is little change to the track forecast reasoning. For the next day or two, Irma or its remnants should move on a north-northwestward to northwestward track along the periphery of a broad mid-level cyclonic gyre. The official forecast is a blend of the latest GFS and ECMWF solutions. KEY MESSAGES: 1. There is the danger of life-threatening storm surge flooding along portions of the coasts of western Florida, Georgia, and South Carolina, where Storm Surge Warnings remain in effect. 2. Irma is producing very heavy rain across the southeastern United States. Intense rainfall rates are leading to flash flooding and rapid rises on creeks, streams, and rivers. Significant river flooding will persist over the Florida peninsula in the wake of Irma and in Georgia, South Carolina and north-central Alabama, where additional heavy rains are expected. Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding. Irma is also expected to produce heavy rains in northern Mississippi and southern portions of Tennessee and North Carolina, where local flooding may occur. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 31.5N 84.0W 45 KT 50 MPH...INLAND 12H 12/0600Z 33.1N 85.5W 35 KT 40 MPH...INLAND 24H 12/1800Z 34.5N 87.3W 30 KT 35 MPH...INLAND 36H 13/0600Z 35.8N 88.8W 25 KT 30 MPH...POST-TROP/INLAND 48H 13/1800Z 37.0N 88.5W 20 KT 25 MPH...POST-TROP/INLAND 72H 14/1800Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Jose Forecast Discussion Number 25

2017-09-11 16:59:04| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Sep 11 2017 000 WTNT42 KNHC 111458 TCDAT2 Hurricane Jose Discussion Number 25 NWS National Hurricane Center Miami FL AL122017 Issued by the NWS Weather Prediction Center College Park MD 1100 AM AST Mon Sep 11 2017 Jose is fighting 25 knots of northeasterly shear this morning according to the UW-CIMSS analysis. A new blowup of deep convection over the center overnight is helping to maintain the satellite-based current intensity estimates, with TAFB and CPHC coming in at 5.0 while SAB had 4.5 and ADT gave 4.6. Have maintained the intensity at 90 kt for this advisory. A 0826z SSMI pass and an 1118z SSMIS pass were quite helpful in determining the analysis position. The analyzed motion for 12z was about 330/12, but Jose should begin trending more northward over the next few hours, if it hasn't already. There is little change to the overall forecast philosophy, as Jose completes a slow anticyclonic loop over open waters for the next 72 hours. The rather odd forecast track is the result of a mid-level high to the east of Jose which will build south of Jose in 24 hours, then west of Jose in about 48 hours, and north of Jose between days 3 and 4. The guidance initially showed this would be a rather tight loop, but has opened it up considerably in the past few runs with the GFS and consensus models beginning to lean toward the ECMWF idea. Have adjusted the forecast track to be closer to the TVCN. By days 4 and 5, Jose should track toward the west- northwest with a bit faster forward motion as the aforementioned mid-level high strengthens to the northeast of Jose. Northerly shear should continue to affect the hurricane for the next couple of days, although there are some differences in the guidance about how strong this shear will be. Have maintained the trend of the previous intensity forecast showing gradual weakening for the next few days. Jose will likely also cross its own wake between days 3 and 4, which is a little later than previously expected with the larger loop depicted in the forecast track. This forecast maintains modest re-intensification at days 4 and 5 as some of the guidance shows the shear relaxing somewhat and the SSTs will be quite warm, although confidence is quite low. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 25.5N 69.1W 90 KT 105 MPH 12H 12/0000Z 26.6N 69.3W 80 KT 90 MPH 24H 12/1200Z 27.1N 68.2W 75 KT 85 MPH 36H 13/0000Z 26.6N 67.0W 70 KT 80 MPH 48H 13/1200Z 25.7N 66.2W 70 KT 80 MPH 72H 14/1200Z 24.1N 67.0W 65 KT 75 MPH 96H 15/1200Z 24.6N 70.6W 70 KT 80 MPH 120H 16/1200Z 26.5N 74.5W 80 KT 90 MPH $$ Forecaster R Ballard

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Tropical Storm Irma Forecast Discussion Number 50

2017-09-11 16:52:48| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Mon Sep 11 2017 000 WTNT41 KNHC 111452 TCDAT1 Tropical Storm Irma Discussion Number 50 NWS National Hurricane Center Miami FL AL112017 1100 AM EDT Mon Sep 11 2017 Irma continues to weaken while moving over extreme northern Florida with most of the deep convection displaced well to the north and northeast of the center due to strong shear. In fact, global model analyses suggest that the system has partial extratropical characteristics, with some associated cold and warm air advection. The current intensity is set at 55 kt which is in line with the highest sustained winds seen in surface observations. Since the cyclone is very large its weakening will be fairly gradual, but the effects of land and shear should reduce the system to a depression in about 24 hours. Shortly thereafter Irma will likely become a remnant low, with complete dissipation by 72 hours as shown by the dynamical guidance. The initial motion continues to be north-northwestward or 340/15 kt. Not much change has been made to the NHC track forecast. Irma or its remnant should continue to move along the eastern and northeastern periphery of a broad mid-level cyclonic circulation until dissipation. The official track forecast is close to the latest corrected multi-model consensus. KEY MESSAGES: 1. There is the danger of life-threatening storm surge flooding along portions of the coasts of Florida, Georgia and South Carolina, where a Storm Surge Warning remains in effect. 2. Irma continues to produce very heavy rain and inland flooding across much of the northern peninsula and eastern panhandle of Florida, and southern Georgia, which is quickly spreading to the rest of the southeast United States. Intense rainfall rates of 2 inches or more per hour is leading 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 southern Georgia, where average rainfall totals of 8 to 15 inches are expected. Significant river flooding is possible beginning Monday and Tuesday in much of central Georgia and southern South Carolina where average rainfall of 3 to 6 inches and isolated 10 inch amounts are expected. Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 30.3N 83.1W 55 KT 65 MPH...INLAND 12H 12/0000Z 32.0N 84.5W 50 KT 60 MPH...INLAND 24H 12/1200Z 33.9N 86.6W 30 KT 35 MPH...INLAND 36H 13/0000Z 35.0N 88.4W 25 KT 30 MPH...POST-TROP/INLAND 48H 13/1200Z 36.0N 89.0W 20 KT 25 MPH...POST-TROP/INLAND 72H 14/1200Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Irma Forecast Discussion Number 49

2017-09-11 11:03:27| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Sep 11 2017 000 WTNT41 KNHC 110903 TCDAT1 Hurricane Irma Discussion Number 49 NWS National Hurricane Center Miami FL AL112017 500 AM EDT Mon Sep 11 2017 Irma is continuing to weaken as it moves across the western Florida peninsula, with the eye dissipating and weakening banding near the center. There are no recent observations of hurricane-force winds near the center, but based on the premise that such winds still exist over the Gulf of Mexico west of the center the initial intensity is reduced to 65 kt. It should be noted that near- hurricane force winds are occurring in a band well northeast of the center with sustained winds of 60 kt reported in the Jacksonville area. The cyclone should continue to weaken as it moves through the southeastern United States, becoming a tropical storm later today, a tropical depression by 36 h, and a remnant low by 48 h. The large-scale models forecast Irma to dissipate completely by 72 h, so the 72 h point has been removed from the forecast. The initial motion is 340/16. The cyclone is expected to move around the eastern side of a mid-level disturbance currently located along the U.S. Gulf Coast, which should cause a north-northwestward to northwestward motion until dissipation. The forecast track takes the center across the eastern Florida Panhandle, southwestern Georgia, eastern and northern Alabama, and eventually into western Tennessee. KEY MESSAGES: 1. There is the danger of life-threatening storm surge flooding along portions of the coasts of Florida, Georgia and South Carolina, where a Storm Surge Warning remains in effect. 2. Irma will continue to bring life-threatening wind impacts to much of central and north Florida, with hurricane-force winds near the center. Also, Irma is a large hurricane, and hurricane-force wind gusts and sustained tropical-storm force winds extend far from the center. Wind hazards from Irma will continue to spread northward through Georgia and into portions of Alabama, Tennessee, South Carolina, and North Carolina. 3. Irma continues to produce very heavy rain and inland flooding across much of the northern peninsula and eastern panhandle of Florida and southern Georgia, which is quickly spreading to the rest of the southeast United States. Intense rainfall rates of 2 inches or more per hour is leading 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 southern Georgia, where average rainfall totals of 8 to 15 inches are expected. Significant river flooding is possible beginning Monday and Tuesday in much of central Georgia and southern South Carolina where average rainfall of 3 to 6 inches and isolated 10 inch amounts are expected. Portions of these states within the southern Appalachians will be especially vulnerable to flash flooding. Farther north and west, Irma is expected to produce average amounts of 2 to 4 inches in parts of Mississippi, Alabama, and Tennessee, northern South Carolina and western North Carolina, where isolated higher amounts and local flooding may occur. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 28.9N 82.6W 65 KT 75 MPH...INLAND 12H 11/1800Z 30.8N 83.7W 55 KT 65 MPH...INLAND 24H 12/0600Z 33.0N 85.7W 35 KT 40 MPH...INLAND 36H 12/1800Z 34.5N 87.8W 25 KT 30 MPH...INLAND 48H 13/0600Z 35.5N 89.0W 20 KT 25 MPH...POST-TROP/INLAND 72H 14/0600Z...DISSIPATED $$ Forecaster Beven

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Hurricane Jose Forecast Discussion Number 24

2017-09-11 10:54:25| National Hurricane Center (Atlantic)

Issued at 500 AM AST Mon Sep 11 2017 000 WTNT42 KNHC 110854 TCDAT2 Hurricane Jose Discussion Number 24 NWS National Hurricane Center Miami FL AL122017 Issued by the NWS Weather Prediction Center College Park MD 500 AM AST Mon Sep 11 2017 Although Jose's satellite appearance is somewhat degraded due to the effects of northeasterly shear estimated to be near 25 kt, it has been able to maintain persistent deep convection over the center. A well-timed 0456Z GPM overpass helped to confirm that the center was on the north side of the cold cloud tops while also highlighting that an eye feature persists despite being obscured in conventional imagery. Subjective and objective satellite-based intensity estimates indicate that Jose continues on a weakening trend, and this supports lowering the initial intensity to 90 kt for this advisory. The initial motion is estimated to be 335/09 kt as Jose continues to track around the western side of a mid-level ridge. As this ridge shifts to the southeast and south of Jose over the next 12 to 24 hours, its forward motion will slow, and the system will begin to move toward the northeast. On days 2 and 3 a ridge will begin to strengthen to the northwest of Jose, driving the system toward the southeast. By day 4 the ridge will move to a position north of Jose, which will gradually accelerate Jose toward the west-northwest through day 5. The expectation is that Jose will complete a small clockwise loop over the open waters of the western Atlantic the next couple of days. Despite the complex forecast track, this general solution is shared by all the reliable model guidance. The official track forecast is shifted slightly north from the previous one due to a northward shift in the ECMWF guidance, and is close to the GFEX consensus model. The northeasterly shear currently over Jose will shift to the northwest and will ease a little, but remain strong enough to keep Jose on a weakening trend through day 3. Although SSTs in the area are warm enough to support an intense hurricane, a slow-moving and looping Jose will likely move over its own cold wake around day 3, as seen in HWRF guidance. On days 4 and 5, Jose will move toward warmer water while the shear relaxes, and there is a potential for reintensification. The latest intensity forecast is very close to the IVCN consensus, but it is more aggressive in weakening Jose than the SHIPS model, which is not accounting for interaction with the cold wake. A 1222Z ASCAT pass sampled Jose nearly perfectly, and the 34/50 kt wind radii were adjusted based on this data. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 24.4N 68.6W 90 KT 105 MPH 12H 11/1800Z 25.8N 69.3W 80 KT 90 MPH 24H 12/0600Z 26.8N 69.0W 75 KT 85 MPH 36H 12/1800Z 27.0N 67.6W 70 KT 80 MPH 48H 13/0600Z 26.3N 66.5W 70 KT 80 MPH 72H 14/0600Z 24.5N 65.5W 65 KT 75 MPH 96H 15/0600Z 25.0N 69.0W 70 KT 80 MPH 120H 16/0600Z 26.5N 73.0W 80 KT 90 MPH $$ Forecaster Birchard

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