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Tropical Storm JULIO Forecast Discussion Number 6

2014-08-05 10:55:33| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE AUG 05 2014 000 WTPZ45 KNHC 050855 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 200 AM PDT TUE AUG 05 2014 Enhanced BD-curve and shortwave infrared imagery reveal little change in the overall cloud pattern of Julio this morning. A partial ASCAT-B scatterometer pass caught the west side of the cyclone and indicated that the winds over the area have actually decreased a bit from yesterday's overpass. Evidently, the 10-15 kt of northeasterly shear continues to impede intensification of the cyclone. Satellite intensity estimates are the same as 6 hours ago, so the initial intensity remains at 50 kt for this advisory. The statistical/dynamical guidance, however, still indicates strengthening through 48 to 60 hours, and both the SHIPS and the Florida State Superensemble (FSSE) show a maximum intensity of 80 kt at that time. Late in the forecast period, Julio is expected to traverse a rather steep sea surface temperature gradient and encounter a more dry and stable air mass intruding from the mid-latitudes of the central Pacific. Both negative contributions should promote a weakening trend. The official intensity forecast follows suit, and is based on a blend of the higher SHIPS and FSSE guidance, which is slightly above the IVCN model. A timely 0523 UTC AMSU MHS microwave image was quite helpful in pinpointing the center of circulation. Julio's initial motion is estimated to be 275/13 kt, within the mid-level easterly flow produced by a mid-tropospheric ridge to the north. This east-to- west oriented ridge is expected to influence a generally westward heading for the next 3 days. For the remainder of the forecast period, global models show a mid-latitude shortwave trough approaching from northwest of the Big Island of Hawaii and eroding the western extent of the ridge. The weakening of the ridge is expected to cause Julio to turn toward west-northwestward through day 5. The NHC forecast is again adjusted slightly to the right, and is very close to the TVCE multi-model consensus and the FSSE corrected consensus. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 13.6N 123.7W 50 KT 60 MPH 12H 05/1800Z 13.9N 125.7W 60 KT 70 MPH 24H 06/0600Z 14.6N 128.6W 65 KT 75 MPH 36H 06/1800Z 15.1N 131.7W 70 KT 80 MPH 48H 07/0600Z 15.7N 134.6W 80 KT 90 MPH 72H 08/0600Z 16.4N 140.4W 80 KT 90 MPH 96H 09/0600Z 17.0N 146.0W 70 KT 80 MPH 120H 10/0600Z 19.0N 152.0W 65 KT 75 MPH $$ Forecaster Roberts

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Hurricane BERTHA Forecast Discussion Number 17

2014-08-05 04:40:17| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT MON AUG 04 2014 000 WTNT43 KNHC 050240 TCDAT3 HURRICANE BERTHA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM EDT MON AUG 04 2014 Bertha certainly does not look like a typical hurricane in satellite imagery this evening. The center has become partially exposed to the northwest of the deep convection. A NOAA Hurricane Hunter aircraft that recently investigated the cyclone observed flight-level, SFMR, and dropsonde winds that all supported hurricane intensity late this afternoon. Since that time, the organization has degraded a little and it is possible that Bertha has weakened below hurricane strength. However, new convection has recently formed just east of the center near where the strongest winds were measured earlier. Therefore, the initial intensity is held at 65 kt. This could be generous, but it is best to maintain hurricane status until the the next Hurricane Hunter aircraft examines the storm around 0600 UTC. Bertha is forecast to gradually weaken during the next day or two while it moves into an area of increasing southwesterly vertical wind shear and over decreasing sea surface temperatures. On Wednesday, the cyclone is expected to interact with an approaching mid-latitude trough and Bertha is forecast to become an extratropical cyclone over the North Atlantic shortly thereafter. Fixes from the aircraft show that Bertha is moving a little faster and has turned north-northeastward this evening. The track forecast reasoning remains unchanged. Bertha is expected to accelerate northeastward during the next day or two between a mid-level ridge over the western Atlantic and a deep-layer trough moving off the northeast United States coast. After Bertha becomes a post-tropical cyclone in 48 to 72 hours, it is forecast to turn east-northeastward in the mid-latitude westerly flow over the north Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 31.3N 73.1W 65 KT 75 MPH 12H 05/1200Z 33.7N 71.9W 60 KT 70 MPH 24H 06/0000Z 36.6N 68.8W 60 KT 70 MPH 36H 06/1200Z 39.3N 64.2W 55 KT 65 MPH 48H 07/0000Z 42.1N 58.9W 55 KT 65 MPH 72H 08/0000Z 47.5N 47.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 09/0000Z 48.5N 31.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 10/0000Z 49.5N 15.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm JULIO Forecast Discussion Number 5

2014-08-05 04:39:45| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON AUG 04 2014 000 WTPZ45 KNHC 050239 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 800 PM PDT MON AUG 04 2014 Conventional satellite imagery and an earlier GCOM AMSR2 microwave overpass show that Julio's cloud pattern continues to gradually improve. Cold tops of -80 C are now evident in association with the developing banding feature south of the center. The AMSR2 pass as well as visible imagery also indicated that deep convection is now wrapping around the northeast portion of the cyclone despite the relatively moderate northeasterly shear. However, the Dvorak subjective and ADT objective satellite intensity estimates remain unchanged from the previous advisory and the initial intensity is held at a conservative 50 kt. No significant changes were made to the intensity forecast from the previous package. However, the forecast now shows a peak intensity of 90 kt at the 48- and 72-hour time frame to correspond more with the SHIPS and Florida State Superensemble. Julio has continued to move at a swift pace this evening and the initial motion is estimated to be 270/14. A mid-tropospheric ridge extending from the southwest United States and Mexico into the eastern Pacific should steer the cyclone on the same heading and at a similar forward speed during the next 4 days. After that time, the large-scale models show the western extent of the ridge weakening in response to a mid-latitude trough approaching the Hawaiian Islands from the northwest. This change in the steering pattern should cause Julio to turn gradually toward the west- northwest, and the model guidance has shifted northward late in the period on this cycle. The NHC track forecast is therefore adjusted northward, and lies just to the south of the TVCE multi- model consensus and the Florida State Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 13.5N 122.8W 50 KT 60 MPH 12H 05/1200Z 13.7N 124.7W 60 KT 70 MPH 24H 06/0000Z 14.2N 127.4W 70 KT 80 MPH 36H 06/1200Z 14.7N 130.3W 80 KT 90 MPH 48H 07/0000Z 15.2N 133.2W 90 KT 105 MPH 72H 08/0000Z 16.0N 138.9W 90 KT 105 MPH 96H 09/0000Z 16.5N 145.0W 80 KT 90 MPH 120H 10/0000Z 18.0N 151.0W 65 KT 75 MPH $$ Forecaster Roberts

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Tropical Storm JULIO Forecast Discussion Number 4

2014-08-04 22:54:25| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON AUG 04 2014 000 WTPZ45 KNHC 042054 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 200 PM PDT MON AUG 04 2014 Tropical Storm Julio has become substantially better organized during the past several hours. Dvorak intensity estimates from TAFB and SAB have increased and now support an initial intensity of 50 kt. A band of deep convection is beginning to wrap most of the way around the circulation, and a 1730 UTC ASCAT pass shows that the low- and mid-level centers are now close to being vertically aligned. Julio has accelerated and the initial motion estimate is now 270/14. A continued westward motion is expected for the next 5 days while the tropical cyclone moves along the southern periphery of a strong ridge over the eastern Pacific. There has been no significant change in the model guidance for this forecast cycle, and the official forecast now lies very near the multi-model consensus. The intensity forecast presents a larger challenge, and several of the models now predict more intensification. DSHP, LGEM, and the HWRF all suggest that Julio will become a hurricane by tomorrow afternoon, which seems reasonable given the recent vertical alignment of the vortex. After that, there is considerable uncertainty as to how much additional strengthening will occur, with DSHP forecasting a 100-kt major hurricane, and GHMI peaking at 70 kt. The official forecast splits these scenarios and peaks at 85 kt, near the intensity consensus. Late in the forecast period, Julio is forecast to pass over cooler SSTs which should lead to weakening. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 13.5N 121.6W 50 KT 60 MPH 12H 05/0600Z 13.4N 123.2W 60 KT 70 MPH 24H 05/1800Z 13.7N 125.9W 70 KT 80 MPH 36H 06/0600Z 14.1N 128.5W 75 KT 85 MPH 48H 06/1800Z 14.6N 131.3W 80 KT 90 MPH 72H 07/1800Z 15.4N 136.8W 85 KT 100 MPH 96H 08/1800Z 16.0N 142.5W 80 KT 90 MPH 120H 09/1800Z 17.0N 149.0W 75 KT 85 MPH $$ Forecaster Zelinsky/Berg

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Hurricane ISELLE Forecast Discussion Number 18

2014-08-04 22:42:38| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON AUG 04 2014 000 WTPZ44 KNHC 042042 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 18...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT MON AUG 04 2014 Corrected quasi-annual to quasi-annular Iselle has an impressive signature on visible satellite imagery with a solid central dense overcast surrounding a 25 n mi wide eye. Final-T estimates from the UW-CIMSS ADT have fallen slightly, but the CI number remains 6.3/122 kt. Along with steady T6.0/115 kt estimates from TAFB and SAB, the initial intensity is held at 120 kt. There is not much change to the intensity forecast. Due to its quasi-annual structure, Iselle should only gradually weaken in the short term while it moves over marginal sea surface temperatures and in a relatively light-shear environment. For that reason, the NHC intensity forecast remains above the intensity guidance for the first 24 hours. Faster weakening is expected thereafter while the cyclone spends about 24 hours over sub-26C water. However, the ocean warms again just to the east of Hawaii, which could allow Iselle to maintain some intensity. After 24 hours, the NHC intensity forecast more closely follows the intensity consensus ICON and the statistical LGEM, which tends to do a good job at the end of the forecast period. Iselle has been moving due westward, or possibly even wobbled just south of due west, during the past few hours. The initial motion estimate is 270/9 kt, but Iselle's forward speed should begin to decrease soon since the ridge to its north has weakened. A mid-level anticyclone is expected to develop and strengthen between California and Hawaii in a day or two, forcing Iselle to turn west-northwestward and accelerate starting in 36 hours. The track guidance has change very little on this cycle, and the updated NHC forecast continues to bring the center of Iselle across the main Hawaiian Islands between 72 and 120 hours. Based on this forecast, Iselle should be crossing 140W just before 1800 UTC on Tuesday. If this forecast holds, then the Central Pacific Hurricane Center in Honolulu, Hawaii, would assume responsibility for Iselle and begin issuing advisories at 2100 UTC, or 11 AM HST on Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 16.1N 137.4W 120 KT 140 MPH 12H 05/0600Z 16.2N 138.5W 115 KT 135 MPH 24H 05/1800Z 16.5N 140.3W 105 KT 120 MPH 36H 06/0600Z 17.1N 142.9W 85 KT 100 MPH 48H 06/1800Z 17.8N 146.1W 70 KT 80 MPH 72H 07/1800Z 19.5N 153.0W 60 KT 70 MPH...NEAR HAWAII 96H 08/1800Z 21.0N 159.0W 55 KT 65 MPH...NEAR HAWAII 120H 09/1800Z 22.5N 164.5W 45 KT 50 MPH...WEST OF HAWAII $$ Forecaster Berg

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