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Hurricane Katia Forecast Discussion Number 6

2017-09-07 04:51:13| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Wed Sep 06 2017 000 WTNT43 KNHC 070251 TCDAT3 Hurricane Katia Discussion Number 6 NWS National Hurricane Center Miami FL AL132017 1000 PM CDT Wed Sep 06 2017 Satellite images indicate that Katia has a small symmetric central dense overcast with very deep convection near the center. Subjective and objective Dvorak estimates have risen since the past advisory and, after accounting for the low bias earlier, support an initial wind speed of 70 kt. With wind shear forecast to drop while the hurricane remains over very warm waters, it is puzzling to see that most of the regional hurricane guidance is only showing a small increase in wind speed. Although this area of the Gulf of Mexico is known for significant upwelling, Katia is a rather small tropical cyclone that shouldn't stir up as much cool water from below as most hurricanes would. After considering the potential upwelling and the extremely favorable upper-level environment, the intensity forecast is raised from the previous one, but could be conservative since the SHIPS RI index is showing roughly a 50 percent of rapid intensification during the next 24 hours. Katia is drifting east-southeastward, caught in a light steering area between two ridges. The hurricane should gradually turn southwestward during the next 24 hours, then accelerate after that time due to a strengthening ridge over the northwestern Gulf of Mexico. The official forecast is very similar to the previous one, on the south side on the dynamical model consensus TVCN in the direction of the corrected consensus. Given the latest wind radii forecast, the government of Mexico has extended the hurricane watch northward to Cabo Rojo. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 21.7N 94.8W 70 KT 80 MPH 12H 07/1200Z 21.5N 94.6W 80 KT 90 MPH 24H 08/0000Z 21.3N 94.8W 90 KT 105 MPH 36H 08/1200Z 21.1N 95.4W 95 KT 110 MPH 48H 09/0000Z 20.6N 96.4W 95 KT 110 MPH 72H 10/0000Z 19.0N 98.5W 20 KT 25 MPH...POST-TROP/INLAND 96H 11/0000Z...DISSIPATED $$ Forecaster Blake

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Hurricane Irma Forecast Discussion Number 31

2017-09-06 22:57:15| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Sep 06 2017 000 WTNT41 KNHC 062057 TCDAT1 Hurricane Irma Discussion Number 31 NWS National Hurricane Center Miami FL AL112017 500 PM AST Wed Sep 06 2017 The eye of Irma passed over the northernmost Virgin Islands earlier this afternoon and it is now located just to their northwest. The satellite and radar presentation of the hurricane remains extremely impressive. An Air Force Reserve reconnaissance aircraft reported peak SFMR winds of 156 kt and flight-level winds of 164 kt during its mission this afternoon. Although there have been no SFMR or flight-level winds as high as what was observed yesterday, the initial intensity remains 160 kt, due to the potential of undersampling. Dropsonde observations in the eye indicated that the pressure rose a few millibars this morning, but the most recent aircraft report shows that the pressure has fallen to 914 mb. The hurricane remains on a west-northwestward motion at about 14 kt. A high pressure ridge over the western Atlantic is forecast to keep Irma on a west-northwestward course over the next 48 to 72 hours. The track guidance is still in good agreement during that period, and little change to the NHC forecast was required. By the weekend, a shortwave trough diving southward over the east-central United States is expected to cause Irma to turn northwestward and northward. The 12Z guidance has generally shifted slightly westward, closer to the previous NHC forecast. As a result, little overall change was made to the 4-5 day track forecast. The NHC track is once again close to the HFIP corrected consensus model. This is also near the 12Z GEFS ensemble mean, but a little east of the latest ECMWF ensemble mean. Users are reminded that the average NHC track errors at days 4 and 5 are about 175 and 225 miles, respectively. 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, and the intensity forecast is again near the upper-end of the guidance and is the same as the previous advisory through 96 hours. Increasingly southwesterly shear and potential land interaction late in the period is expected to cause some decrease in Irma's strength by day 5. Efforts to provide the forecast models with as much data as possible continue, with 6-hourly NWS balloon launches across much of the continental United States, and the NOAA G-IV aircraft currently sampling the environment around the storm. 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 could be issued for portions of the Florida Keys and the Florida peninsula on Thursday. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 18.8N 65.4W 160 KT 185 MPH 12H 07/0600Z 19.6N 67.6W 155 KT 180 MPH 24H 07/1800Z 20.7N 70.4W 150 KT 175 MPH 36H 08/0600Z 21.5N 73.1W 145 KT 165 MPH 48H 08/1800Z 22.2N 75.6W 140 KT 160 MPH 72H 09/1800Z 23.2N 79.0W 135 KT 155 MPH 96H 10/1800Z 26.0N 80.2W 125 KT 145 MPH 120H 11/1800Z 31.0N 81.0W 105 KT 120 MPH $$ Forecaster Brown

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Hurricane Katia Forecast Discussion Number 5

2017-09-06 22:54:15| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Wed Sep 06 2017 000 WTNT43 KNHC 062054 TCDAT3 Hurricane Katia Discussion Number 5 NWS National Hurricane Center Miami FL AL132017 400 PM CDT Wed Sep 06 2017 An Air Force reconnaissance plane just investigated Katia and found a much better organized tropical cyclone with a partial eyewall. It also measured a flight-level wind of 71 kt and 66 kt with the SFMR. Based on these data and the improved satellite presentation, Katia is upgraded to a hurricane with 65 kt winds. The upper-level wind pattern is becoming more favorable, and that can be observed by the expansion of the outflow. All models continue to favor intensification, and in fact, the SHIPS RI index gives a 63 percent chance of a 30-kt wind increase in 24 hours. The NHC forecast calls for strengthening but at this time is not as high as some of the guidance. Katia is embedded within very weak steering currents, and it is now moving slowly toward the southeast at about 3 kt. The hurricane is forecast to meander in the southwestern Gulf of Mexico for the next day or two. After that time the global models develop a ridge over the northern Gulf of Mexico and this flow pattern will steer Katia southwestward toward the state of Veracruz. The NHC forecast is basically on top of the multi-model consensus and follows the trend of the HFIP corrected consensus HCCA. Given the upward intensity trend and the forecast track toward the coast, the government of Mexico has issued a hurricane watch for a portion of the coast of the state of Veracruz. Katia is also forecast to bring torrential rains primarily to the state of Veracruz during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 21.7N 95.1W 65 KT 75 MPH 12H 07/0600Z 21.5N 94.7W 70 KT 80 MPH 24H 07/1800Z 21.3N 94.7W 75 KT 85 MPH 36H 08/0600Z 21.1N 95.0W 80 KT 90 MPH 48H 08/1800Z 20.9N 95.9W 80 KT 90 MPH 72H 09/1800Z 19.5N 98.0W 25 KT 30 MPH...POST-TROP/INLAND 96H 10/1800Z...DISSIPATED $$ Forecaster Avila

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Hurricane Jose Forecast Discussion Number 6

2017-09-06 22:38:50| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Sep 06 2017 000 WTNT42 KNHC 062038 TCDAT2 Hurricane Jose Discussion Number 6 NWS National Hurricane Center Miami FL AL122017 500 PM AST Wed Sep 06 2017 Jose has continued to become better organized. Banding convection has become very symmetric around the center, and the upper-level outflow has become well established in all quadrants, despite the presence of Hurricane Irma to the west. An eye-like dimple has occasionally been observed in visible imagery during the afternoon. The initial intensity is now 65 kt, based on the latest Dvorak intensity estimate from TAFB. There is no reason to believe that the recent intensification trend will end soon. In fact, the SHIPS Rapid Intensification Index gives a 48 percent chance of intensification of 30 kt (or more) in the next 24 h. My forecast is just shy of that, and is close to the intensification rate shown by the HWRF for the next 36 h. After about 48-72 h, the vertical wind shear is forecast to increase, and all of the models forecast weakening. Overall, the NHC forecast is a little above the model consensus for the first 72 h, but close to IVCN by the end of the forecast. A pair of late-arriving ASCAT passes and recent visible imagery indicate that Jose is a little farther north than previously estimated. The initial motion estimate is 285/14 kt. Due to the northward shift of the initial position, the forecast has been adjusted in that direction for the first 48 h. However, the reasoning behind the forecast has not changed, and Jose should continue on a fairly steady west-northwest track, steered primarily by the subtropical ridge. After that time, a mid-level trough should cause the ridge to retreat eastward, allowing Jose to gain more latitude. The global models, especially the ECMWF, are suggesting that this turn may occur a little later than previously expected, and have shifted westward a little bit. The new NHC forecast at 96 and 120 h is very close to a blend of the GFS and ECMWF models, and is about a degree west of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 13.9N 45.8W 65 KT 75 MPH 12H 07/0600Z 14.5N 48.0W 75 KT 85 MPH 24H 07/1800Z 15.1N 51.1W 90 KT 105 MPH 36H 08/0600Z 15.8N 54.0W 95 KT 110 MPH 48H 08/1800Z 16.4N 56.4W 100 KT 115 MPH 72H 09/1800Z 18.5N 60.2W 100 KT 115 MPH 96H 10/1800Z 21.5N 63.7W 85 KT 100 MPH 120H 11/1800Z 25.0N 67.5W 70 KT 80 MPH $$ Forecaster Zelinsky

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Hurricane Irma Forecast Discussion Number 30

2017-09-06 16:48:09| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 06 2017 000 WTNT41 KNHC 061448 TCDAT1 Hurricane Irma Discussion Number 30 NWS National Hurricane Center Miami FL AL112017 1100 AM AST Wed Sep 06 2017 The eye of Irma passed over Barbuda, St. Barthelemy, and St. Martin this morning, and will be moving over portions of the British and U.S. Virgin Islands shortly. A NOAA National Ocean Service observing site on Barbuda measured sustained winds of 103 kt with a gust to 135 kt earlier this morning before the anemometer failed. The station also reported a minimum pressure of 916.1 mb. A minimum pressure of 915.9 mb was reported on St. Barthelemy. An Air Force reconnaissance aircraft that performed a single pass through the eye this morning reported SFMR winds of 152 kt in the northwestern eyewall around 12Z. Assuming there are stronger winds in the northeastern eyewall, the initial intensity remains 160 kt for this advisory. Another Air Force aircraft is currently entering the storm. Irma is moving west-northwestward or 285/14 kt. A strong high pressure ridge extending from the central Atlantic westward is expected to keep Irma moving west-northwestward during the next 2 to 3 days. The track guidance is in good agreement during this period and the NHC track is along the southern edge of the guidance envelope in best agreement with the ECMWF and HFIP corrected consensus model. After that time, a shortwave trough moving southward over the east-central United States is expected to erode the western portion of the ridge. As a result, Irma is forecast to turn northwestward and northward, but there is still a fair amount of uncertainty regarding the exact timing and location of recurvature. The NHC forecast has been shifted eastward to be in better agreement with the latest model guidance, however it should be noted that there are numerous GEFS and ECMWF ensemble members that take Irma over and/or west of Florida. The updated NHC track is in best agreement with the latest ECMWF ensemble mean. Users are reminded that the average NHC track errors at days 4 and 5 are about 175 and 225 statue miles, respectively. Irma is forecast to remain within favorable atmospheric conditions and over warm waters during the next 3 to 4 days. Therefore, Irma is likely to remain a very powerful hurricane during this time, and the NHC intensity forecast is unchanged from the previous advisory through day 4. Since the 120-h forecast point is now offshore, the intensity forecast at that time has been adjusted accordingly. Now that Irma's eye is clearly visible in radar imagery from San Juan, Tropical Cyclone Updates with hourly position estimates will be issued starting at 1200 PM AST (1600 UTC). KEY MESSAGES: 1. Irma is a potentially catastrophic category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to portions of the northern Leeward Islands, including the Virgin Islands and Puerto Rico today. 2. A hurricane warning is in effect for the northern coast of the Dominican Republic, the southeastern Bahamas, the Turks and Caicos, and portions of Haiti, with a hurricane watch in effect for the central Bahamas and much of Cuba. Irma is likely to bring dangerous wind, storm surge, and rainfall to some of these areas tonight through Friday. 3. Irma could directly affect the remainder of the Bahamas and Cuba as an extremely dangerous major hurricane later this week. Residents in these areas should monitor the progress of Irma and listen to advice given by officials. 4. Direct impacts from wind, storm surge, and rainfall are possible in the Florida Keys and portions of the Florida Peninsula beginning later this week and this weekend. However, given the forecast uncertainty at these time ranges, it is too soon to specify the location and magnitude of these impacts. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 18.2N 64.0W 160 KT 185 MPH 12H 07/0000Z 19.0N 66.2W 155 KT 180 MPH 24H 07/1200Z 20.2N 69.0W 150 KT 175 MPH 36H 08/0000Z 21.2N 71.7W 145 KT 165 MPH 48H 08/1200Z 21.9N 74.2W 140 KT 160 MPH 72H 09/1200Z 22.9N 78.1W 135 KT 155 MPH 96H 10/1200Z 25.2N 80.0W 125 KT 145 MPH 120H 11/1200Z 29.0N 80.5W 110 KT 125 MPH $$ Forecaster Brown

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