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Hurricane Irma Forecast Discussion Number 33

2017-09-07 11:03:19| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 07 2017 000 WTNT41 KNHC 070903 TCDAT1 Hurricane Irma Discussion Number 33 NWS National Hurricane Center Miami FL AL112017 500 AM AST Thu Sep 07 2017 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, and the Turks and Caicos and southeastern and central Bahamas tonight and Friday. 2. Hurricane watches are in effect for the northwestern Bahamas and 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

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Hurricane Jose Forecast Discussion Number 8

2017-09-07 10:55:48| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 07 2017 000 WTNT42 KNHC 070855 TCDAT2 Hurricane Jose Discussion Number 8 NWS National Hurricane Center Miami FL AL122017 500 AM AST Thu Sep 07 2017 Enhanced BD-curve infrared imagery indicates some improvement of the inner core during the past several hours. The earlier identified banding eye feature in microwave imagery appears to be closing off in the west side. Based on the overall improvement of the cloud pattern and a consensus of the satellite intensity estimates from TAFB and SAB, the initial intensity is raised to 80 kt. Further strengthening is forecast during the next 36 hours. After that time, increasing northerly shear associated with the outflow of Hurricane Irma should inhibit further intensification and subsequently, cause the cyclone to begin weakening. The intensity forecast is based primarily on the IVCN consensus model and is close to the HWRF through 48 hours. The initial motion is estimated to be west-northwestward, or 285/16 kt, within the mid-tropospheric flow produced by the western extent of a subtropical high to the north. Jose should continue on this general west-northwestward track through the 36 hour period. Afterward, the ridge to the north is forecast to weaken in response to a mid-latitude shortwave trough approaching from the northeast. This transition in the synoptic steering pattern should influence Jose in a more northwestward motion through the remainder of the forecast period. The NHC forecast is slightly to the left of the previous advisory beyond 48 hours, and is based on a blend of the HFIP Corrected consensus model and the ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 14.8N 49.1W 80 KT 90 MPH 12H 07/1800Z 15.2N 51.5W 90 KT 105 MPH 24H 08/0600Z 15.8N 54.7W 100 KT 115 MPH 36H 08/1800Z 16.4N 57.5W 110 KT 125 MPH 48H 09/0600Z 17.2N 59.5W 100 KT 115 MPH 72H 10/0600Z 19.7N 63.2W 90 KT 105 MPH 96H 11/0600Z 23.0N 67.0W 70 KT 80 MPH 120H 12/0600Z 26.4N 69.1W 60 KT 70 MPH $$ Forecaster Roberts

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Hurricane Katia Forecast Discussion Number 7

2017-09-07 10:37:20| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Thu Sep 07 2017 000 WTNT43 KNHC 070837 TCDAT3 Hurricane Katia Discussion Number 7 NWS National Hurricane Center Miami FL AL132017 400 AM CDT Thu Sep 07 2017 Katia has not changed appreciably during the past several hours with a small central dense overcast and a curved banding feature in the northeastern quadrant. Satellite estimates are about the same as earlier, so the initial wind speed will stay at 70 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to be in the hurricane in a few hours to get a better estimate of the current intensity. Katia is forecast to be over very warm waters with decreasing shear for the next 24-36 hours. Thus strengthening is expected as long as the center remains offshore. It is still puzzling why most of the guidance don't intensify this much, but since the global models continue to show significant deepening, the official forecast will stay on the high side of the guidance. The hurricane is essentially stationary, waiting for a ridge to build over the northwestern Gulf to steer Katia southwestward at a faster pace. Most of the guidance are in agreement on this track, although the UKMET is a notable outlier showing more of a westward motion. The only significant change from the previous advisory is to speed up the track of Katia as it approaches the coast. Given the latest track forecast, the government of Mexico has issued a Hurricane Warning for the previous Hurricane Watch area. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 21.5N 94.5W 70 KT 80 MPH 12H 07/1800Z 21.5N 94.5W 80 KT 90 MPH 24H 08/0600Z 21.2N 95.0W 90 KT 105 MPH 36H 08/1800Z 20.8N 95.8W 90 KT 105 MPH 48H 09/0600Z 20.2N 97.1W 70 KT 80 MPH...INLAND 72H 10/0600Z 19.5N 99.0W 15 KT 15 MPH...POST-TROP/INLAND 96H 11/0600Z...DISSIPATED $$ Forecaster Blake

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Hurricane Jose Forecast Discussion Number 7

2017-09-07 04:59:18| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 06 2017 000 WTNT42 KNHC 070259 TCDAT2 Hurricane Jose Discussion Number 7 NWS National Hurricane Center Miami FL AL122017 1100 PM AST Wed Sep 06 2017 Jose's deep convection displays a tightly curved band that wraps at least twelve-tenths around the center. Dvorak intensity estimates from both TAFB and SAB have increased accordingly. Thus, maximum sustained winds are analyzed for Jose at 75 kt, very close to that from the CIMSS Advanced Dvorak Technique. Jose is likely to continue developing during the next day or two while the vertical shear is low, the SSTs are around 29C, and the mid-level humidity is moist. However, beginning in two to three days, the outflow from large, strong hurricane Irma to Jose's west should start inducing more shear, inducing a steady weakening by days four and five. The official intensity forecast is based upon a blend of the LGEM, HWRF, and COAMPS models. Jose's anticipated peak intensity of 105 kt is slightly higher than the previous advisory, while days four and five show a more quickly weakening system at that time. The hurricane is moving toward the west-northwest around 15 kt, as it is being advected along the south side of the deep-layer Bermuda high. This motion should continue for the next couple of days. During days three to five, Jose should bend toward the northwest as it moves around the periphery of the Bermuda high. The official track forecast is based upon the very tightly clustered guidance (and their consensus technique - TVCN), which is somewhat west of the previous advisory. If future guidance further shifts westward, then tropical storm or hurricane watches may be required for portions of the Leeward Islands on Thursday. Jose is a small hurricane with tropical-storm-force winds extending out at most 70 nm from the center, based upon NDBC Buoy 41041 and the 0006Z ASCAT-A scatterometer pass. The official size foreast - based upon the RVCN consensus - suggests a gradual increase in size for the next three days. Interestingly, buoy 41041 measured a peak 1-minute wind (at 5 m anemometer height) of 61 kt around 22Z. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 14.4N 47.5W 75 KT 85 MPH 12H 07/1200Z 14.9N 49.8W 85 KT 100 MPH 24H 08/0000Z 15.5N 53.0W 95 KT 110 MPH 36H 08/1200Z 16.1N 55.8W 105 KT 120 MPH 48H 09/0000Z 16.8N 58.2W 100 KT 115 MPH 72H 10/0000Z 19.3N 62.0W 90 KT 105 MPH 96H 11/0000Z 22.4N 65.8W 75 KT 85 MPH 120H 12/0000Z 25.9N 68.4W 60 KT 70 MPH $$ Forecaster Landsea

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Hurricane Irma Forecast Discussion Number 32

2017-09-07 04:57:16| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 06 2017 000 WTNT41 KNHC 070257 TCDAT1 Hurricane Irma Discussion Number 32 NWS National Hurricane Center Miami FL AL112017 1100 PM AST Wed Sep 06 2017 Earlier radar observations from the San Juan WSR-88D showed a concentric eyewall, and observations from an Air Force Hurricane Hunter aircraft showed a secondary wind maximum over the northwest quadrant. These phenomena may be associated with some weakening, but since the central pressure hasn't risen much the intensity is held at 160 kt at this time. Moreover, the concentric eyewall has become less apparent in recent radar imagery. Considerable lightning activity has been noted in the eyewall of Irma, which research has shown to sometimes be a harbinger of weakening. Notwithstanding, low vertical wind shear and warm waters along the forecast track of Irma should allow it to remain a very powerful hurricane during the next several days. The official intensity forecast is similar to the previous one except at day 5 when stronger shear should cause more weakening. This forecast is generally above the intensity model consensus. Irma continues on a west-northwestward heading at around 14 kt. A ridge of high pressure over the western Atlantic should maintain this course for the next 48 to 72 hours. Later in the forecast period a shortwave trough moving into the southeastern United States is likely to turn the hurricane northwestward to north-northwestward. There has been a slight eastward shift in some of the track guidance models, but since the models could shift back to the west it is prudent to make little change to the official forecast at this time. In any event, users are reminded not to focus on the exact track since the average NHC track errors at days 4 and 5 are about 175 and 225 miles, respectively. KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to Puerto Rico tonight, the northern coast of Hispaniola Thursday, and the Turks and Caicos and southeastern and central Bahamas Thursday and Friday. 2. Hurricane watches are in effect for the northwestern Bahamas and 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 has increased. Hurricane watches will likely be issued for portions of the Florida Keys and the Florida peninsula on Thursday. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 19.4N 66.8W 160 KT 185 MPH 12H 07/1200Z 20.3N 68.8W 155 KT 180 MPH 24H 08/0000Z 21.3N 71.7W 150 KT 175 MPH 36H 08/1200Z 22.1N 74.1W 145 KT 165 MPH 48H 09/0000Z 22.7N 76.3W 140 KT 160 MPH 72H 10/0000Z 24.0N 79.3W 135 KT 155 MPH 96H 11/0000Z 27.4N 80.3W 120 KT 140 MPH 120H 12/0000Z 32.0N 81.0W 95 KT 110 MPH $$ Forecaster Pasch

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