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Hurricane GONZALO Forecast Discussion Number 10

2014-10-14 22:41:05| National Hurricane Center (Atlantic)

Issued at 500 PM AST TUE OCT 14 2014 000 WTNT43 KNHC 142041 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 PM AST TUE OCT 14 2014 Data from an Air Force Reserve Hurricane Hunter aircraft earlier today indicated flight-level and SFMR wind data that were just below the threshold of a major hurricane. On the last flight leg, the aircraft measured a central pressure of 971 mb, which was down 2 mb from what was measured at the start of the mission. The eye had also contracted from a 20 nmi diameter down to about 16 nmi on the last report. Recent data from the NOAA Doppler radar in San Juan indicate that the eye has contracted to about 15 nmi at an altitude of about 36,000 ft since the aircraft departed a few hours ago, signifying that the eye diameter is likely smaller at lower altitudes. In addition, satellite imagery indicates that the eye has cleared out and warmed while cloud tops have cooled significantly in the surrounding eyewall. Based on the trends noted in the radar and satellite data, the intensity has been increased to 100 kt, which is supported by a UW-CIMSS ADT value of T5.4/100 kt. Gonzalo continues to move steadily northwestward with a motion of 320/11 kt. The NHC model guidance is tightly packed and remains is in excellent agreement on Gonzalo moving steadily northwestward around the periphery of a deep-layer ridge located to its north during the next 36 hours or so. By 48 hours, a deep mid-tropospheric trough and cold front are expected to move eastward across the Bahamas and weaken the western portion of the ridge. This should allow the cyclone to turn slowly northward, and then accelerate northeastward by 72 hours ahead of the aforementioned trough and front, with the hurricane potentially threatening Bermuda on Day 3. Gonzalo is expected to merge with the cold front or become extratropical by 120 hours. The new track forecast is just an update of the previous advisory track, and lies close to a blend of the GFEX and TVCA consensus models. With the eye of Gonzalo having contracted and become more distinct in satellite, radar, and recon wind data, the system appears primed for intensification into a category 4 hurricane later tonight or on Wednesday. Sea-surface temperatures ahead of the cyclone are sufficiently warm enough at 28C-28.5C to support a category 4 hurricane through at least the next 36 hours. The global models continue to indicate that the best vertical shear conditions and 200 mb upper-level outflow pattern are expected to occur on Wednesday and continue into Thursday morning. Afterwards, eyewall cycles and possible cold upwelling beneath the hurricane are likely to cause some fluctuations in the intensity. By 72 hours, increasing vertical wind shear ahead of the aforementioned deep trough is expected to induce weakening. By 120 hours, Gonzalo will be over sub-20C SSTs in the North Atlantic and experiencing vertical shear of 50-60 kt, which should result in the cyclone becoming an extratropical low. The NHC intensity forecast is similar to the previous advisory and remains above all of the available intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 21.2N 66.0W 100 KT 115 MPH 12H 15/0600Z 22.5N 67.1W 110 KT 125 MPH 24H 15/1800Z 24.0N 68.2W 115 KT 130 MPH 36H 16/0600Z 25.4N 68.7W 120 KT 140 MPH 48H 16/1800Z 27.2N 68.3W 110 KT 125 MPH 72H 17/1800Z 32.0N 65.6W 100 KT 115 MPH 96H 18/1800Z 39.9N 60.4W 85 KT 100 MPH 120H 19/1800Z 49.0N 50.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane GONZALO Forecast Discussion Number 9

2014-10-14 17:00:38| National Hurricane Center (Atlantic)

Issued at 1100 AM AST TUE OCT 14 2014 000 WTNT43 KNHC 141500 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 1100 AM AST TUE OCT 14 2014 Data from an Air Force Reserve Hurricane Hunter aircraft and the San Juan Doppler weather radar indicate that the earlier intensification process has abated, which is apparently due to some shear-induced disruption of the eye. Maximum 700 mb flight-level winds observed thus far are 112 kt and maximum SFMR winds through most of the morning have been around 93 kt. The central pressure has also leveled off during the past few hours at around 973 mb. A blend of the flight-level surface-wind conversion and SFMR winds support maintaining an intensity of 95 kt. Gonzalo continues to move northwestward with a motion of 315/11 kt. There is no significant change to the previous forecast track or reasoning. The NHC model guidance is in excellent agreement on the hurricane continuing to move northwestward around the southwestern for periphery of a deep-layer ridge the during the next 36 hours. After that, the western portion of the ridge is expected to weaken as a strong mid-latitude trough and associated cold front currently located over the southeastern U.S. moves eastward across the Bahamas by 48 hours. The increasing southwesterly flow ahead of those systems should gradually accelerate Gonzalo toward the northeast, with the cyclone potentially threatening Bermuda in about three days' time. Gonzalo is expected to merge with the strong cold front or become extratropical by 120 hours. The new track forecast is similar to the previous advisory track, and lies close to a blend of the GFEX and TVCA consensus models. Recent radar and satellite data indicate that the eye of Gonzalo has been clearing out and gradually becoming better defined with a diameter of about 20 nmi. Once the eyewall stabilizes again, intensification will likely resume, and in fact the reconnaissance aircraft a few moments ago observed an SFMR wind of 99 kt that suggests this intensification is beginning. Buoy data indicate that water temperatures are slightly cooler than what the SHIPS model is indicating, probably due to cold upwelling created by the wake of former Hurricane Fay, but they are still sufficiently warm enough to support a category 4 hurricane. The best vertical shear conditions and upper-level outflow regime are expected to occur on Wednesday and into Thursday morning, and that is when Gonzalo is expected to strengthen into a category 4 hurricane. Afterwards, eyewall cycles and possible cold upwelling beneath the hurricane are likely to cause some fluctuations in the intensity. By 72 hours, increasing southwesterly wind shear ahead of the aforementioned deep trough and strong cold front is expected to induce weakening. By 120 hours, Gonzalo should be over cold waters of the North Atlantic and experiencing vertical shear of more than 50 kt, which should result in the cyclone becoming a extratropical low. The NHC intensity forecast is similar to the previous advisory and is above all of the available intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 20.3N 65.2W 95 KT 110 MPH 12H 15/0000Z 21.7N 66.4W 100 KT 115 MPH 24H 15/1200Z 23.3N 67.8W 110 KT 125 MPH 36H 16/0000Z 24.6N 68.6W 120 KT 140 MPH 48H 16/1200Z 26.1N 68.6W 115 KT 130 MPH 72H 17/1200Z 30.4N 66.5W 105 KT 120 MPH 96H 18/1200Z 37.4N 62.6W 90 KT 105 MPH 120H 19/1200Z 46.8N 53.8W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane GONZALO Forecast Discussion Number 8

2014-10-14 10:55:33| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE OCT 14 2014 000 WTNT43 KNHC 140855 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 AM AST TUE OCT 14 2014 Air Force Hurricane Hunter aircraft data indicate that Gonzalo has continued to quickly strengthen overnight while the eye has passed just northeast of the British Virgin Islands. The aircraft measured a peak flight-level wind of 116 kt in the northeastern eyewall and SFMR surface winds of 92 kt. A blend of these data yield an initial intensity of 95 kt for this advisory. The SHIPS model and a UW-CIMSS shear analysis show about 15 to 20 kt of south- southwesterly shear over Gonzalo, which may be why the eye has not become apparent in infrared imagery. The shear is forecast to decrease and remain low during the next few days while the hurricane moves over warm water. This should allow for additional strengthening during the next 12 to 24 hours. Eyewall cycles are likely to cause some fluctuations in intensity after that time. In about 3 days, gradual weakening is predicted to begin as Gonzalo will be moving over gradually decreasing sea surface temperatures and into an area of increasing southwesterly shear. The updated NHC intensity forecast is close to the SHIPS guidance, and is a little higher than the previous advisory through 72 hours due to the higher initial intensity. Gonzalo is moving northwestward or 315/11 kt. The hurricane is expected to remain on a northwestward heading during the next 24 to 36 hours. After that time, Gonzalo should turn northward, then north-northeastward ahead a mid-latitude trough that is forecast to move off the east coast of the United States in 2 to 3 days. Late in the period, the hurricane should accelerate northeastward in deep layer southwesterly flow over the North Atlantic. The track guidance is in good agreement on this scenario, but there remains some spread in the forward speed of the hurricane after 72 hours. The new NHC track forecast is similar to the previous advisory and is close to the GFEX and TVCA consensus models. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 19.6N 64.4W 95 KT 110 MPH 12H 14/1800Z 21.0N 65.6W 105 KT 120 MPH 24H 15/0600Z 22.7N 67.1W 110 KT 125 MPH 36H 15/1800Z 24.1N 68.3W 115 KT 130 MPH 48H 16/0600Z 25.4N 68.7W 110 KT 125 MPH 72H 17/0600Z 28.9N 67.3W 105 KT 120 MPH 96H 18/0600Z 34.5N 64.0W 95 KT 110 MPH 120H 19/0600Z 43.5N 56.5W 85 KT 100 MPH $$ Forecaster Brown

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Hurricane GONZALO Forecast Discussion Number 7

2014-10-14 04:42:35| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON OCT 13 2014 000 WTNT43 KNHC 140242 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 1100 PM AST MON OCT 13 2014 The eye of Gonzalo moved just north of St. Maarten and over Anguilla earlier this evening. St. Maarten reported a peak 2-minute wind of 55 kt and a gust of 65 kt with a minimum pressure of 994 mb. Data from the Hurricane Hunter aircraft earlier indicated peak 700-mb flight-level winds of around 85 kt, which support an intensity of 75 kt for this advisory. This intensity is also supported by the latest Dvorak classification of T4.5 from TAFB. The next Hurricane Hunter aircraft will be investigating Gonzalo around 0600 UTC. Gonzalo appears to be poised to intensify, perhaps rapidly, in the next day or so. The inner-core features are quite distinct in recent microwave imagery and a warm spot has recently developed in infrared imagery with a more symmetric cloud pattern. Given these trends and the overall favorable environment, the intensity forecast has been adjusted upward and is close to the the SHIPS model on the high end of the intensity guidance through the first 48 hours, showing Gonzalo becoming a major hurricane in about 36 hours. As Gonzalo gains latitude later in the period, southwesterly shear ahead of a mid-latitude trough and cooler SSTs should result in gradual weakening. The eye of Gonzalo is now evident in WSR-88D imagery from San Juan, and the initial motion estimate is 315/10. Overall, the track forecast reasoning remains unchanged, as the hurricane will move northwestward into a weakness in the subtropical ridge and then accelerate northward and northeastward ahead of a mid-latitude trough moving off the east coast of the United States. The new NHC track forecast has been shifted a little to the right in the first 48 hours due to the initial position and motion and an adjustment and toward the latest multi-model consensus. Beyond that time, the new NHC forecast is largely and update of the previous one and is close to but a bit slower than a blend of the GFS and ECMWF models, especially by day 5. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 18.7N 63.4W 75 KT 85 MPH 12H 14/1200Z 19.8N 64.7W 85 KT 100 MPH 24H 15/0000Z 21.5N 66.1W 95 KT 110 MPH 36H 15/1200Z 23.1N 67.4W 100 KT 115 MPH 48H 16/0000Z 24.5N 68.1W 105 KT 120 MPH 72H 17/0000Z 27.3N 67.9W 100 KT 115 MPH 96H 18/0000Z 31.5N 65.5W 95 KT 110 MPH 120H 19/0000Z 37.0N 61.0W 85 KT 100 MPH $$ Forecaster Brennan

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Hurricane GONZALO Forecast Discussion Number 6

2014-10-13 22:56:30| National Hurricane Center (Atlantic)

Issued at 500 PM AST MON OCT 13 2014 000 WTNT43 KNHC 132056 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 PM AST MON OCT 13 2014 Another Air Force Reserve reconnaissance aircraft investigating Gonzalo this afternoon recently found 700-mb maximum flight-level winds of 77 kt along with believable SFMR surface winds of 62-67 kt in the northeastern quadrant, plus a central pressure of 984 mb. Based on these data, the intensity has been increased to 65 kt, making Gonzalo the sixth hurricane of the 2014 Atlantic hurricane season. Note that some higher SFMR winds were observed, but these were believed to be contaminated by shallow-water shoaling. The initial motion estimate is 305/10 kt. The center of Gonzalo has been developing northward on the Guadeloupe radar while the entire circulation has been moving west-northwestward. The result is now a northwestward motion, which is expected to continue for the next 36 hours or so. After that time, Gonzalo is forecast to gradually turn northward as a break in the subtropical to its north develops by 48-72 hours. On days 4 and 5, the hurricane is forecast to accelerate to the northeast as the southwesterly flow ahead of fast-moving deep-layer trough and associated cold front that is currently located over the south-central United States. The models are in better agreement on this track scenario with only a minor eastward shift noted through 36 hours. After that, however, the models have made a significant westward shift and now bring Gonzalo very close to Bermuda in the 96-120 hour time period. The official forecast track lies close to a blend of the GFEX and TVCN consensus models through 48 hours, and is a little to the right of the consensus models at 72-120 hours. Both the radar and satellite presentations of Gonzalo continue to improve, with a 20 n mi diameter eye noted in the radar data since about 1400-1500 UTC. Gonzalo has been strengthening at a rate of 20-25 kt since this time yesterday. Given that current environmental and oceanic conditions are expected to remain essentially unchanged for the next 48 hours, a similar rate of strengthening is forecast during that time, with Gonzalo forecast to become a major hurricane by 48 hours. After that, gradually increasing southwesterly vertical wind shear ahead of the aforementioned deep-layer trough is expected to induce gradual weakening. The NHC intensity forecast remains above the intensity consensus models, and closely follows the SHIPS intensity model. Although hurricane conditions are not currently expected in the U.S. Virgin Islands, only a slight deviation to the left of the forecast track, or a more rapid strengthening of the storm, would result in the need to extend the hurricane warning into those areas. Interests in the hurricane watch area are reminded that the watch means that hurricane conditions are possible, and in this case within the next 12-18 hours. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 17.9N 62.9W 65 KT 75 MPH 12H 14/0600Z 18.8N 64.1W 70 KT 80 MPH 24H 14/1800Z 20.5N 65.7W 80 KT 90 MPH 36H 15/0600Z 22.2N 67.1W 90 KT 105 MPH 48H 15/1800Z 23.8N 68.2W 100 KT 115 MPH 72H 16/1800Z 26.3N 68.5W 100 KT 115 MPH 96H 17/1800Z 30.0N 66.4W 95 KT 110 MPH 120H 18/1800Z 35.0N 62.8W 90 KT 105 MPH $$ Forecaster Stewart

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