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Hurricane BERTHA Forecast Discussion Number 16

2014-08-04 22:42:10| National Hurricane Center (Atlantic)

Issued at 500 PM EDT MON AUG 04 2014 000 WTNT43 KNHC 042042 TCDAT3 HURRICANE BERTHA DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 PM EDT MON AUG 04 2014 Bertha continues to have a disorganized appearance on satellite imagery. A small burst of deep convection is occurring just east of the center, and the system continues to have well-defined upper-level outflow over the southeastern quadrant. A NOAA Hurricane Hunter aircraft is currently investigating the tropical cyclone, and we shall soon see if Bertha is maintaining hurricane status. Based on wind data from an Air Force mission earlier this afternoon, which showed a slight decrease, the current intensity is reduced to 65 kt. Flight-level wind data from that earlier mission also showed that the circulation had a very small extent over the northwestern quadrant, and high-resolution visible imagery shows low clouds moving northwestward, away from the center, not far from the center over that quadrant. This suggests that, if the environmental low-level flow increases, Bertha may have a difficult time maintaining a closed circulation. For now, the NHC intensity forecast calls for gradual weakening, and is a little below most of the guidance since the shear is predicted to become prohibitively strong, 50 kt or more, in just 36 hours. Fixes from the aircraft showed a gradual increase in forward speed and the initial motion is around 360/15. There are no important changes to the track forecast or reasoning. During the next couple of days, Bertha will be moving between a mid-level high pressure area over the southwestern Atlantic and a broad trough moving off the northeast United States coast. This should result in a gradual turn toward the north-northeast and northeast with additional acceleration during the next 24-48 hours. Later in the forecast period, Bertha or its post-tropical counterpart should accelerate east-northeastward in the mid-latitude westerlies over the north Atlantic. The official forecast is similar to the previous one and lies between the latest GFS and ECMWF tracks. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 29.4N 73.6W 65 KT 75 MPH 12H 05/0600Z 31.8N 72.8W 65 KT 75 MPH 24H 05/1800Z 34.7N 70.7W 65 KT 75 MPH 36H 06/0600Z 37.5N 67.0W 60 KT 70 MPH 48H 06/1800Z 40.0N 62.0W 55 KT 65 MPH 72H 07/1800Z 47.0N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 08/1800Z 49.0N 37.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 09/1800Z 49.0N 24.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Storm JULIO Forecast Discussion Number 3

2014-08-04 16:40:45| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON AUG 04 2014 000 WTPZ45 KNHC 041440 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 800 AM PDT MON AUG 04 2014 Julio remains sharply sheared from the northeast, and deep convection is limited to the western half of the circulation. A blend of Dvorak estimates from TAFB, SAB, and UW-CIMSS supports holding the initial intensity at 40 kt. The global dynamical guidance suggests that moderate northwesterly shear will continue for at least the next 24 to 36 hours, which should limit the rate at which the tropical cyclone can strengthen. After that, the environment is forecast to become more favorable, and the members of IVCN unanimously indicate that Julio will become a hurricane within 72 hours. By days 4 and 5, the intensity is expected to level off while the cyclone encounters cooler SSTs due to a combination of the sharp SST gradient to the northwest, and a possible cold wake from Hurricane Iselle. The initial motion remains 270/11. The track forecast reasoning is unchanged and Julio is still expected to be steered generally west-northwestward by a strong ridge over the eastern Pacific. A slightly more northward component to the motion is expected later in the forecast period while Julio encounters a slight weakness in the mid-level ridge. The track guidance has shifted north again so the NHC track forecast has been nudged northward accordingly. However, it remains slightly south of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 13.5N 119.4W 40 KT 45 MPH 12H 05/0000Z 13.3N 121.5W 45 KT 50 MPH 24H 05/1200Z 13.4N 124.0W 50 KT 60 MPH 36H 06/0000Z 13.7N 126.6W 55 KT 65 MPH 48H 06/1200Z 14.1N 129.3W 65 KT 75 MPH 72H 07/1200Z 15.0N 134.7W 75 KT 85 MPH 96H 08/1200Z 15.7N 140.4W 80 KT 90 MPH 120H 09/1200Z 16.5N 146.5W 80 KT 90 MPH $$ Forecaster Zelinsky/Berg

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Hurricane BERTHA Forecast Discussion Number 15

2014-08-04 16:39:39| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT MON AUG 04 2014 000 WTNT43 KNHC 041439 TCDAT3 HURRICANE BERTHA DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 AM EDT MON AUG 04 2014 In spite of its unimpressive appearance on satellite imagery, with scant evidence of banding features and relatively disorganized deep convection, aerial reconnaissance data indicate that Bertha has intensified into a hurricane. Flight-level, dropsonde, and SFMR winds from Air Force and NOAA Hurricane Hunter planes support an intensity of 70 kt for this advisory. Bertha does have well-defined anticyclonic upper-level outflow over the eastern and southern portions of the circulation. Recent infrared imagery shows warming cloud tops, so the intensity is probably leveling off. Dynamical guidance predicts a very large increase in shear beginning in 24-36 hours, and a weakening trend is forecast to begin around that time. In about 72 hours, the global models show the cyclone interacting with a baroclinic zone in the vicinity of Newfoundland, so the NHC forecast shows Bertha becoming extratropical by that time. Center fixes from the Hurricane Hunter aircraft indicate that the motion is now 360/15 kt. The track forecast remains relatively straightforward. Over the next couple of days, Bertha should turn toward the northeast and accelerate in the flow between a mid-tropospheric anticyclone over the southwestern Atlantic and a broad trough moving off the United States east coast. Later in the forecast period, the cyclone should continue moving quickly to the northeast or east-northeast within the mid-latitude westerlies. The official forecast track is not much different from the previous one, and close to the dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 27.6N 73.6W 70 KT 80 MPH 12H 05/0000Z 30.0N 73.4W 70 KT 80 MPH 24H 05/1200Z 33.4N 72.1W 70 KT 80 MPH 36H 06/0000Z 36.3N 69.3W 65 KT 75 MPH 48H 06/1200Z 39.0N 65.0W 60 KT 70 MPH 72H 07/1200Z 45.0N 55.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 08/1200Z 49.0N 45.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 09/1200Z 49.0N 33.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane ISELLE Forecast Discussion Number 17

2014-08-04 16:37:04| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON AUG 04 2014 000 WTPZ44 KNHC 041436 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT MON AUG 04 2014 Iselle continues to intensify and has reached category 4 strength. Convective cloud tops as cold as -75C surround the eye, which has grown to a diameter of 25-30 n mi. Dvorak estimates were a consensus T6.0/115 kt from TAFB and SAB at 1200 UTC, and the objective UW-CIMSS ADT has crept up to T6.3/122 kt since that time. Based on these estimates, the initial intensity is raised to 120 kt. Vertical shear is expected to remain light for the next 24 hours or so while Iselle moves over gradually cooler SSTs. Since Iselle has some characteristics of an annular hurricane, it is likely to change little in intensity during the next day or so, and even when it begins to weaken, the trend should be gradual. On day 3, Iselle will be moving over the coldest water (between 25 and 26C) along its forecast track, and vertical shear is expected to increase to about 15-20 kt. Both factors should induce quicker weakening at that time. The NHC intensity forecast remains above all of the typically used intensity models during the first 24 hours, is very close to the consensus on days 2-3, and then more closely follows the decay shown by the LGEM model toward the latter part of the forecast period. Iselle's initial motion is 275/9 kt. A mid- to upper-level shortwave trough is swinging by to the north of the hurricane and eroding the subtropical ridge, which should cause Iselle to slow down a bit during the next 24 hours. After that time, a mid-level high is forecast to develop and strengthen between Hawaii and California, forcing Iselle to turn west-northwestward and accelerate as it approaches and moves near the Hawaiian Islands. The track guidance has been stable and tightly clustered for a few cycles now, and no significant changes were required to the NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 16.2N 136.5W 120 KT 140 MPH 12H 05/0000Z 16.2N 137.7W 115 KT 135 MPH 24H 05/1200Z 16.3N 139.2W 110 KT 125 MPH 36H 06/0000Z 16.8N 141.4W 95 KT 110 MPH 48H 06/1200Z 17.4N 144.2W 80 KT 90 MPH 72H 07/1200Z 19.0N 150.5W 60 KT 70 MPH...EAST OF HAWAII 96H 08/1200Z 21.0N 157.0W 50 KT 60 MPH...NEAR HAWAII 120H 09/1200Z 22.5N 162.0W 45 KT 50 MPH...WEST OF HAWAII $$ Forecaster Berg

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Tropical Storm BERTHA Forecast Discussion Number 14

2014-08-04 10:57:38| National Hurricane Center (Atlantic)

Issued at 500 AM EDT MON AUG 04 2014 000 WTNT43 KNHC 040857 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 AM EDT MON AUG 04 2014 Convection has been pulsing near the center, but the overall convective cloud pattern of Bertha has changed little since the previous advisory due to moderate northwesterly wind shear. Earlier Air Force Reserve reconnaissance wind data around 0500 UTC supported a 55-kt intensity, especially since the pressure had decreased 3 mb down to 1004 mb. However, a NOAA research aircraft has just started its investigation of the cyclone, and surface wind data support increasing the intensity to 60 kt along with a central pressure fall to about 999 mb. Bertha is now moving northward or 350/14 kt. There remains no significant change to the previous track forecast or reasoning. The latest NHC model guidance remains tightly clustered and in excellent agreement on Bertha continuing to move around the western periphery of the Bermuda-Azores high pressure ridge for the next 36 hours or so, followed by a northeastward acceleration into the mid-latitude westerlies ahead of a deep-layer trough and frontal system currently approaching the U.S. east coast. The official forecast track is just a tad to the left of the previous advisory, and is close to the consensus model TVCA. The 72-, 96-, and 120-hour positions are based on a blend of input from the NOAA Ocean Prediction Center. On the forecast track, Bertha is expected to pass about midway between the U.S. coast and Bermuda on Tuesday. The northwesterly vertical wind shear that has been plaguing Bertha for the past few days is now decreasing and is gradually backing around to a southwesterly direction. In fact, the global models indicate that Bertha will move underneath a 200 mb ridge axis in 18-24 hours, at which time we should see the cyclone reach hurricane status. That intensity should be short-lived since the shear is forecast to increase to more than 30 kt by 48 hours and beyond, which should induce at least steady weakening. The intensity, however, has been held higher than normal due to Bertha's expected transition to an extratropical cyclone with possible baroclinic energy keeping the system fairly strong. Extratropical transition is expected by 72 hours, but it could occur sooner due to 50 kt or more of shear and SSTs around 20C by that time. The NHC intensity forecast is similar to the previous advisory, remaining above the consensus models ICON and IVCN, and is close to a blend of the SHIPS and LGEM intensity models. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 26.1N 73.6W 60 KT 70 MPH 12H 04/1800Z 28.6N 73.7W 60 KT 70 MPH 24H 05/0600Z 31.9N 72.9W 65 KT 75 MPH 36H 05/1800Z 35.0N 70.8W 65 KT 75 MPH 48H 06/0600Z 37.7N 67.0W 60 KT 70 MPH 72H 07/0600Z 43.4N 57.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 08/0600Z 47.5N 47.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 09/0600Z 49.5N 37.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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