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Hurricane GONZALO Forecast Discussion Number 15

2014-10-16 04:58:48| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED OCT 15 2014 000 WTNT43 KNHC 160258 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 1100 PM AST WED OCT 15 2014 Although satellite images have recently shown increased organization, aircraft data suggest that Gonzalo has actually slightly weakened. An Air Force Reserve Hurricane Hunter aircraft measured peak flight-level winds of 118 kt and a peak SFMR value of 99 kt. These data support an initial intensity of 105 kt. The plane did report that the concentric eyewall cycle has finished, suggesting that the weakening trend is probably over. Little change in strength is shown for the next 24 hours since the shear expected to be weak or moderate while the hurricane traverses warm waters. Gradual weakening is shown after that time due to the cyclone moving across cooler waters, some of which were upwelled by the recent passage of Fay near Bermuda. The official NHC forecast is a little lower than the previous one, although is on the higher side of the guidance during the first 36 hours. Transition to a post-tropical cyclone is expected in about 72 hours with most of the models showing Gonzalo becoming a large warm-seclusion low. Gonzalo is turning northward as it feels the effects of a strong trough over the eastern United States. There is good agreement on the cyclone moving toward the north-northeast tomorrow and northeast on Friday, accelerating as it is steered by the trough. The NHC forecast virtually unchanged over the first couple of days of the prediction, with most of the models showing Gonzalo near Bermuda in a little over 36 hours. At longer range, the extratropical cyclone should move more to the east-northeast as it moves within the fast mid-latitude flow to the north of a central Atlantic ridge. Only small changes were made to the previous forecast, which ends up being slightly slower at days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 24.6N 68.7W 105 KT 120 MPH 12H 16/1200Z 25.8N 68.7W 105 KT 120 MPH 24H 17/0000Z 28.1N 68.0W 105 KT 120 MPH 36H 17/1200Z 30.7N 66.6W 100 KT 115 MPH 48H 18/0000Z 33.8N 64.8W 90 KT 105 MPH 72H 19/0000Z 43.8N 57.4W 80 KT 90 MPH...POST-TROPICAL 96H 20/0000Z 52.0N 37.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 21/0000Z 55.0N 17.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake

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Hurricane GONZALO Forecast Discussion Number 14

2014-10-15 22:45:41| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED OCT 15 2014 000 WTNT43 KNHC 152045 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 PM AST WED OCT 15 2014 Gonzalo is not quite as well organized as it was this morning. Satellite images show that the eye of the hurricane appears less distinct than it was earlier today, and radar images from a NOAA hurricane hunter aircraft earlier today suggested than the inner eyewall could be eroding. The initial wind speed is lowered to 110 kt based on the slightly degraded appearance of the storm. Another Air Force reconnaissance aircraft is scheduled to investigate Gonzalo this evening and should provide a better assessment of its intensity and structure. The hurricane remains on track and is moving northwestward at about 9 kt. Water vapor images show a large trough over the eastern United States. This trough is expected to move eastward during the next couple of days, which should cause Gonzalo to make a turn toward the north on Thursday and north-northeast on Friday, likely bringing Gonzalo near Bermuda in about 2 days. After that time, a faster northeastward and then east-northeastward motion is predicted over the North Atlantic Ocean. The track model guidance, in general, is a little slower than it was at 1200 UTC and the official forecast has been adjusted accordingly. The guidance is also not quite as tightly clustered as it has been, as the ECMWF has shifted a bit west of the rest of the primary objective aids. The large scale environmental conditions are expected to remain favorable during the next day or so, and the intensity of Gonzalo will likely fluctuate due to eyewall replacement cycles. In about 48 hours, the hurricane is expected to be moving into an atmosphere of increasing southwesterly shear and drier air, and over sharply colder waters. These conditions should cause weakening and post-tropical transition in 3 to 4 days. NOAA buoy 41046 recently reported a pressure of 955 mb, and was quite useful in estimating Gonzalo's minimum pressure. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 24.1N 68.6W 110 KT 125 MPH 12H 16/0600Z 25.3N 68.9W 110 KT 125 MPH 24H 16/1800Z 27.2N 68.6W 105 KT 120 MPH 36H 17/0600Z 29.7N 67.2W 105 KT 120 MPH 48H 17/1800Z 32.9N 65.3W 100 KT 115 MPH 72H 18/1800Z 41.8N 58.4W 80 KT 90 MPH 96H 19/1800Z 51.0N 42.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 20/1800Z 54.0N 20.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Hurricane GONZALO Forecast Discussion Number 13

2014-10-15 16:54:39| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED OCT 15 2014 000 WTNT43 KNHC 151454 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 1100 AM AST WED OCT 15 2014 Data from an Air Force reconnaissance aircraft indicate that Gonzalo has strengthened a little. The maximum 700 mb flight-level wind reported was 123 kt and the highest SFMR wind observation was 116 kt. Based on these data, the initial wind speed is increased to 115 kt, making Gonzalo a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. This is the first category 4 hurricane in the Atlantic basin since Ophelia in 2011. The aircraft data and microwave images clearly show concentric eyewalls, with the inner radius of maximum wind now only about 4-5 n mi from the center. Smoothing through the trochoidal oscillation of the eye yields an initial motion estimate of 320/10 kt. A high amplitude trough over the eastern United States is expected to slowly move eastward during the next couple of days, and will erode the subtropical ridge that is currently steering Gonzalo. This change in the large-scale pattern should cause the hurricane to turn northward by early Thursday and north-northeastward Thursday night and Friday, likely bringing Gonzalo near Bermuda in about 2 days. Beyond 48 hours, the hurricane is forecast to accelerate generally northeastward. The track model guidance remains tightly clustered, and the official forecast is near the GFS and ECMWF solutions and only slightly to the left of the previous one. Given the evidence of concentric eyewalls, and with the inner eyewall already about as small as it can get, the current period of intensification could be about over. The hurricane will likely fluctuate in strength while the environmental conditions remain favorable during the next day or two. After that time, weakening is forecast when the hurricane moves into an atmosphere of increasing southwesterly shear and drier air, and over much colder water. Post-tropical transition will likely occur in 3 to 4 days when the cyclone is forecast to cross the north wall of the Gulf Stream current. Little change was made to the previous intensity forecast, and this one lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 23.5N 68.0W 115 KT 130 MPH 12H 16/0000Z 24.6N 68.7W 115 KT 130 MPH 24H 16/1200Z 26.3N 68.9W 115 KT 130 MPH 36H 17/0000Z 28.6N 68.0W 110 KT 125 MPH 48H 17/1200Z 31.6N 66.2W 105 KT 120 MPH 72H 18/1200Z 40.6N 60.8W 90 KT 105 MPH 96H 19/1200Z 50.5N 46.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 20/1200Z 54.0N 24.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Hurricane GONZALO Forecast Discussion Number 12

2014-10-15 10:50:08| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED OCT 15 2014 000 WTNT43 KNHC 150850 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 AM AST WED OCT 15 2014 The small eye of Gonzalo has become a little less distinct in infrared satellite imagery overnight. It is possible that an eye wall replacement has begun, but there has been no recent microwave images to assess the current structure of the inner core. There has been little change in the subjective and objective Dvorak satellite intensity estimates overnight and the initial wind speed remains 110 kt for this advisory. Another Air Force Reserve reconnaissance aircraft is en route to the hurricane, which should provide a better assessment of the intensity of Gonzalo this morning. A UW/CIMSS shear analysis and the SHIPS model indicate that there is still some light to moderate southerly shear over the hurricane, but the shear is expected to decrease today. This favors intensification, however difficult-to-predict eye wall replacement cycles could cause some fluctuations in intensity during the next day or two. The NHC forecast calls for some slight intensification today followed by little change in strength in 24 to 48 hours. After that time, increasing southwesterly shear, drier air, and cooler sea surface temperatures should cause weakening. Gonzalo is expected to become extratropical by day 4, and the global models indicate that it will remain a powerful extratropical low through the end of the forecast period. Gonzalo is moving northwestward or 320/11 kt. The forecast track reasoning remains unchanged. The hurricane should turn north- northwestward and northward during the next day or so as it moves around the western side of a mid-level ridge over the central Atlantic. After that time, Gonzalo is forecast to turn north-northeastward and accelerate ahead of a mid-latitude trough that will be moving off the east coast of the United States. The track guidance is in excellent agreement on this scenario, however the updated NHC forecast has been shifted a little west of the previous advisory to be closer to the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 22.9N 67.3W 110 KT 125 MPH 12H 15/1800Z 24.0N 68.3W 115 KT 130 MPH 24H 16/0600Z 25.5N 68.9W 115 KT 130 MPH 36H 16/1800Z 27.3N 68.5W 110 KT 125 MPH 48H 17/0600Z 29.9N 67.1W 105 KT 120 MPH 72H 18/0600Z 37.5N 62.8W 90 KT 105 MPH 96H 19/0600Z 48.5N 52.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 20/0600Z 54.0N 30.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Hurricane GONZALO Forecast Discussion Number 11

2014-10-15 05:15:11| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE OCT 14 2014 000 WTNT43 KNHC 150315 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 1100 PM AST TUE OCT 14 2014 Data from an Air Force Hurricane Hunter reconnaissance aircraft indicate that Gonzalo has continued to strengthen. The plane reported maximum flight-level of 125 kt in the northeastern quadrant and peak SFMR winds of 108 kt. The minimum surface pressure also has fallen about 17 mb during the last 9 hours to 954 mb. Satellite images show that the eye has warmed and shrunk to a diameter of 8 n mi while the inner core has generally become better defined. However, Gonzalo has been maintaining an asymmetric distribution of convection, presumably due to around 15 kt of south-southwesterly shear of affecting the cyclone according to the latest SHIPS and UW-CIMSS shear analyses. A blend of the flight- level and SFMR wind data is used to raise the initial intensity of 110 kt. Water vapor imagery and cloud-tracked wind vectors show an upper- level trough between Bermuda and the southeastern U.S. responsible for the south-southwesterly shear over Gonzalo, but the shear should not be enough to prevent additional intensification from taking place over warm waters of 28-29 deg C during the next day or so. At some point during this time, fluctuations in strength due to difficult-to-forecast inner core evolution are probable. By 72 hours, a significant increase in south-southwesterly shear should induce a considerable weakening trend. Increasing baroclinicity in the near-storm environment, much cooler waters, and drier and more stable air wrapping around the hurricane's circulation should result in extratropical transition by day 4. The NHC intensity forecast is about the same as the previous one, and is near or higher than the highest intensity guidance (SHIPS/LGEM) through 36 hours but close to the multi-model consensus after that. Gonzalo has continued to move on a northwestward course, or 320/11, though the center has wobbled a bit toward the left during the last couple of hours. The hurricane should gradually turn north- northwestward and then northward and slow down as it moves around the western periphery of an eastward-shifting central Atlantic ridge during the next 24 to 36 hours. By 48 hours, Gonzalo should encounter a deep-layer south-southwesterly flow associated with a potent mid-latitude trough swinging out of the east-central United States. This flow pattern should turn Gonzalo north-northeastward with increasing forward speed. Although the track guidance is tightly clustered through 72 hours, there is still some along-track spread in the model solutions, with the ECMWF depicting a weaker and much-slower-moving cyclone. The new NHC forecast places less weight on the ECMWF, owing to Gonzalo's current intensity. The official NHC forecast lies on the far eastern side of the guidance envelope and to the right of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 22.2N 66.6W 110 KT 125 MPH 12H 15/1200Z 23.4N 67.6W 120 KT 140 MPH 24H 16/0000Z 24.9N 68.5W 120 KT 140 MPH 36H 16/1200Z 26.3N 68.7W 115 KT 130 MPH 48H 17/0000Z 28.5N 67.7W 110 KT 125 MPH 72H 18/0000Z 34.7N 64.1W 100 KT 115 MPH 96H 19/0000Z 45.1N 56.7W 80 KT 90 MPH...POST-TROP/EXTRATROP 120H 20/0000Z 52.5N 42.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Kimberlain

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