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Hurricane Katia Forecast Discussion Number 9

2017-09-07 22:34:24| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Thu Sep 07 2017 000 WTNT43 KNHC 072034 TCDAT3 Hurricane Katia Discussion Number 9 NWS National Hurricane Center Miami FL AL132017 400 PM CDT Thu Sep 07 2017 Katia has changed little in organization since this morning, with limited convective banding features. An eye has not yet become apparent in satellite imagery. The current intensity is held at 70 kt which is roughly the mean of Dvorak estimates from TAFB and SAB. An Air Force Reserve Unit Hurricane Hunter aircraft is scheduled to investigate Katia this evening to check its intensity. Global models continue to show a well-developed upper-level outflow structure tonight and Friday, and strengthening is likely prior to landfall. The official intensity forecast is above the model consensus, and it is possible that Katia will approach major hurricane status prior to crossing the coast of Mexico early Saturday. Comparing afternoon satellite position estimates to reconnaissance center fixes from this morning, there does not appear to have been much motion today. A mid-level ridge is forecast to build to the north of Katia during the next day or so. This should cause Katia to move generally southwestward, and make landfall in Mexico in 36 hours or so. The official track forecast has been shifted just slightly southward and is mainly a blend of the latest simple and corrected consensus guidance tracks. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 21.6N 94.6W 70 KT 80 MPH 12H 08/0600Z 21.3N 95.0W 80 KT 90 MPH 24H 08/1800Z 20.9N 95.6W 90 KT 105 MPH 36H 09/0600Z 20.3N 96.7W 90 KT 105 MPH 48H 09/1800Z 19.5N 97.6W 40 KT 45 MPH...INLAND 72H 10/1800Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Irma Forecast Discussion Number 34

2017-09-07 16:52:16| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Sep 07 2017 000 WTNT41 KNHC 071452 TCDAT1 Hurricane Irma Discussion Number 34 NWS National Hurricane Center Miami FL AL112017 1100 AM AST Thu Sep 07 2017 The eye on satellite continues to be quite distinct, and data from an Air Force reconnaissance plane indicate that the initial intensity is 150 kt. The central pressure remains near 921 mb. 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 will not remain a powerful hurricane for the next 3 days while approaching Florida. Thereafter, an increase in the wind shear could lead to gradual weakening, but Irma is expected to remain a major hurricane until landfall occurs. The best estimate of the initial motion is toward the west-northwest or 290 degrees at 14 kt. Irma is being steered by the flow around the south side of the subtropical ridge, but in 2 to 3 days, the hurricane will be located on the southwestern edge of the aforementioned ridge, and a turn to the northwest and north- northwest should then begin. There has been no change in the guidance which is still quite clustered and brings the core of Irma very near the southeast Florida coast in about 3 days. The NHC forecast, which is similar to the previous one, is very close to the multi-model consensus and the HFIP corrected consensus HCCA. The later has been performing very well during Irma. 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 today. These hazards will spread across the Turks and Caicos tonight and the Bahamas tonight through Saturday. 2. A hurricane watch is in effect for much of Cuba. Irma is likely to bring dangerous wind, storm surge, and rainfall to portions of these areas on Friday and Saturday. 3. The threat of dangerous major hurricane impacts in Florida continues to increase. A hurricane watch has been issued for south Florida, the Florida Keys, Lake Okeechobee, and Florida Bay. This watch will likely be expanded northward later today. Residents in these areas should heed any advice given by local officials. 4. A storm surge watch has also been issued 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. 5. The chance of direct impacts is increasing in portions of Georgia, South Carolina, and North Carolina, but it is too early to specify the magnitude and location of the impacts. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 20.4N 69.7W 150 KT 175 MPH 12H 08/0000Z 21.1N 71.7W 145 KT 165 MPH 24H 08/1200Z 21.9N 74.2W 140 KT 160 MPH 36H 09/0000Z 22.5N 76.5W 135 KT 155 MPH 48H 09/1200Z 23.1N 78.4W 135 KT 155 MPH 72H 10/1200Z 25.5N 80.0W 125 KT 145 MPH 96H 11/1200Z 30.1N 80.6W 105 KT 120 MPH 120H 12/1200Z 35.0N 82.0W 50 KT 60 MPH...INLAND $$ Forecaster Avila

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Hurricane Jose Forecast Discussion Number 9

2017-09-07 16:50:21| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Sep 07 2017 000 WTNT42 KNHC 071450 TCDAT2 Hurricane Jose Discussion Number 9 NWS National Hurricane Center Miami FL AL122017 1100 AM AST Thu Sep 07 2017 Jose is developing an eye. Convection remains very symmetric around the center, and a well-defined mid-level eye has been evident in microwave imagery throughout the morning. Outflow remains well established in all quadrants, despite the close proximity of Irma to the west, perhaps in part due to the small size of Jose. The initial intensity has been held at 80 kt, based on the latest Dvorak classifications from TAFB and SAB. However, the overall trend of intensification is not likely to have ended, and Jose is still forecast to become a major hurricane in about 24 h. After about 48 h, most of the intensity guidance indicates that Jose will begin to weaken, but the extent of that weakening varies quite a bit, in part due to uncertainty surrounding how much the shear from a deep-layer trough to the north and Irma may affect Jose after it passes the Leeward Islands. The official forecast is still close to the HWRF for the first 36 h, and close to the intensity consensus, IVCN, after that. The initial motion remains 285/16 kt. Almost no change has been made to the first 36 h of the forecast, and the hurricane is still expected to continue west-northwestward, along the southern extent of the subtropical ridge. Beyond that time, the global models suggest that an approaching mid-latitude trough will cause the ridge to retreat, causing Jose to turn more toward the northwest, and eventually toward the north. Based on the lastest model runs, this turn may happen a little later than previously expected. Thus, the NHC official forecast has been nudged toward the west at days 3-5, and is close to the multi-model consensus, TVCX. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 14.9N 50.6W 80 KT 90 MPH 12H 08/0000Z 15.4N 53.1W 90 KT 105 MPH 24H 08/1200Z 16.0N 56.0W 100 KT 115 MPH 36H 09/0000Z 16.6N 58.5W 105 KT 120 MPH 48H 09/1200Z 17.5N 60.5W 100 KT 115 MPH 72H 10/1200Z 20.3N 64.4W 85 KT 100 MPH 96H 11/1200Z 24.0N 67.5W 75 KT 85 MPH 120H 12/1200Z 27.0N 68.5W 65 KT 75 MPH $$ Forecaster Zelinsky

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Hurricane Katia Forecast Discussion Number 8

2017-09-07 16:32:47| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Thu Sep 07 2017 000 WTNT43 KNHC 071432 TCDAT3 Hurricane Katia Discussion Number 8 NWS National Hurricane Center Miami FL AL132017 1000 AM CDT Thu Sep 07 2017 An Air Force Hurricane Hunter aircraft found that the central pressure had dropped to 982 mb and maximum SFMR-observed surface winds were close to 70 kt. Therefore 70 kt will be retained for the current intensity. Vertical wind shear should remain low over the southwest Gulf of Mexico for the next couple of days and the global models show well-developed upper-level outflow over the tropical cyclone. Thus, further strengthening is likely up to landfall. The official intensity forecast is somewhat higher than the model consensus and Katia could approach major hurricane status before it crosses that coast. Fixes from the Hurricane Hunter aircraft show essentially no motion over the last several hours. A mid-level ridge is likely to build to the north of Katia during the next day or so. This should induce a west-southwestward motion beginning tonight or early Friday, leading to landfall by late Friday or early Saturday. The official track forecast is similar to the previous one and close to the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 21.6N 94.6W 70 KT 80 MPH 12H 08/0000Z 21.4N 95.0W 80 KT 90 MPH 24H 08/1200Z 21.2N 95.5W 90 KT 105 MPH 36H 09/0000Z 20.7N 96.5W 90 KT 105 MPH 48H 09/1200Z 19.9N 97.9W 40 KT 45 MPH...INLAND 72H 10/1200Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Irma Forecast Discussion Number 33

2017-09-07 12:54:49| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 07 2017 000 WTNT41 KNHC 071054 CCA TCDAT1 Hurricane Irma Discussion Number 33...Corrected NWS National Hurricane Center Miami FL AL112017 500 AM AST Thu Sep 07 2017 Corrected to modify Key Messages to reflect the issuance of a hurricane warning for the northwestern Bahamas. Irma has become a little less organized during the past few hours. Data from an Air Force reserve Hurricane Hunter aircraft near 0500 UTC indicated that the central pressure had risen to 921 mb and that the winds had decreased both at the 700 mb flight-level and in surface estimates from the Stepped Frequency Microwave Radiometer. Since that time, the eye has become cloud filled and the central convection has become somewhat ragged. The initial intensity is lowered to 155 kt, and this could be a little generous. The next aircraft is scheduled to reach Irma around 1200 UTC. The initial motion is 290/15. The hurricane is currently being steered by the subtropical ridge to the north, and for the next 48 h or so this motion is expected to continue with a decrease in the forward speed. After 48 h, a mid- to upper-level trough digging into the eastern United States is expected to create a break in the ridge and allow Irma to turn northward. The timing of the turn is the most important question and one still filled with uncertainty. The UKMET, UK Ensemble mean, and the NAVGEM are the models showing the latest turn, and they forecast Irma to move into the southeastern Gulf of Mexico and near the west coast of the Florida Peninsula. The ECMWF and ECMWF Ensemble mean are in the middle of the model pack and show Irma moving over the southeastern portion of the Florida Peninsula. The GFS, Canadian, and GFS Ensemble mean show the earliest turn and show Irma moving east of the coast of Florida toward the southeastern United States. The new forecast track will best follow the ECMWF, as well as the Florida State Superensemble and the HFIP Corrected Consensus, and it calls for the center to move over portions of the southeastern Florida Peninsula between 72-96 h and then across the Atlantic into southern South Carolina by 120 h. Users are again reminded not to focus on the exact track since the average NHC track errors at days 3, 4, and 5 are about 120, 175, and 225 miles, respectively. Irma should remain in warm-water, and a low shear environment for about the next three days, and thus is expected to remain a strong hurricane, most likely Category 5 or 4. Fluctuations in intensity are likely during the time due to internal eyewall replacement cycles. The large-scale models suggest that shear could increase starting at about 72 hr. However, due to the uncertainty as to whether this will happen, the intensity forecast keeps Irma at category 4 strength until landfall in Florida. The 96-120 h points now have a lower intensity due to the forecast of shear and land interaction, but Irma is still expected to be a hurricane when it reaches the southeastern United States. Since Irma is moving away from Puerto Rico and the radars there, the hourly position estimates are discontinued after this advisory. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to the northern coast of Hispaniola today, the Turks and Caicos tonight, and the Bahamas tonight through Saturday. 2. A hurricane watch is in effect much of Cuba. Irma is likely to bring dangerous wind, storm surge, and rainfall to portions of these areas on Friday and Saturday. 3. The threat of direct hurricane impacts in Florida over the weekend and early next week continues to increase. Hurricane watches will likely be issued for portions of the Florida Keys and the Florida peninsula later this morning. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 20.0N 68.3W 155 KT 180 MPH 12H 07/1800Z 20.7N 70.5W 150 KT 175 MPH 24H 08/0600Z 21.7N 73.1W 145 KT 165 MPH 36H 08/1800Z 22.3N 75.5W 140 KT 160 MPH 48H 09/0600Z 22.8N 77.4W 135 KT 155 MPH 72H 10/0600Z 24.5N 80.0W 130 KT 150 MPH 96H 11/0600Z 28.5N 80.5W 105 KT 120 MPH 120H 12/0600Z 33.0N 81.0W 75 KT 85 MPH...INLAND $$ Forecaster Beven/Brennan

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