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Tropical Storm BERTHA Forecast Discussion Number 22

2014-08-06 10:46:05| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED AUG 06 2014 000 WTNT43 KNHC 060846 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 AM AST WED AUG 06 2014 Deep convection continues to pulse downshear of the center of Bertha, as the tropical cyclone is situated in a favorable region for forced ascent in the equatorward entrance region of an upper- level jet streak. The initial intensity remains 45 kt based on the Dvorak classification from TAFB and an earlier ASCAT pass that showed some 40-45 kt winds east of the center. As Bertha becomes embedded in the jet, the vertical shear will increase in the next 12 to 24 hours. This should result in the low-level circulation decoupling from the convection while the cyclone becomes embedded in a baroclinic zone. Bertha should be post-tropical by 24 hours, and then gradually decay as an extratropical cyclone. Bertha is expected to be absorbed by day 5, although this could occur sooner. The latest satellite fixes indicate an initial motion of 055/24. Bertha is well embedded in deep-layer southwesterly flow ahead of a mid-latitude trough, and will continue moving northeastward over the north Atlantic for the next day or so before turning eastward by 72 hours. The new NHC track is largely an update of the previous one, and is close to guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 39.0N 65.4W 45 KT 50 MPH 12H 06/1800Z 40.8N 61.7W 45 KT 50 MPH 24H 07/0600Z 43.6N 55.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 07/1800Z 46.0N 49.9W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 08/0600Z 48.0N 44.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 09/0600Z 48.5N 28.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 10/0600Z 48.5N 12.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 11/0600Z...ABSORBED $$ Forecaster Brennan

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Tropical Storm BERTHA Forecast Discussion Number 21

2014-08-06 04:42:06| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE AUG 05 2014 000 WTNT43 KNHC 060241 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM AST TUE AUG 05 2014 Bertha briefly became devoid of thunderstorm activity late this afternoon, however a new burst of deep convection has developed to the northeast of the center this evening. The initial wind speed remains 45 kt and is based on a Dvorak classification of T3.0 from TAFB. The vertical shear over Bertha has increased to more than 40 kt and is expected to increase even further by Wednesday. Despite the shear, little overall change in strength is predicted during the next 24 hours since Bertha will transform into an extratropical low and gain some energy from baroclinic processes during that time. The latest fixes indicate that Bertha has turned northeastward with a motion of 045/20 kt. The cyclone should continue northeastward during the next 48 hours ahead of a mid-latitude trough that is moving off the northeast United States coast. Later in the forecast period, the post-tropical cyclone is predicted to move east-northeastward to eastward in mid-latitude westerly flow over the North Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 37.5N 68.1W 45 KT 50 MPH 12H 06/1200Z 39.5N 64.5W 45 KT 50 MPH 24H 07/0000Z 42.2N 58.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 07/1200Z 45.0N 52.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 08/0000Z 47.3N 47.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 09/0000Z 48.5N 33.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 10/0000Z 48.5N 17.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 11/0000Z...ABSORBED BY EXTRATROPICAL LOW $$ Forecaster Brown

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Tropical Storm JULIO Forecast Discussion Number 9

2014-08-06 04:39:07| National Hurricane Center (East Pacific)

Issued at 800 PM PDT TUE AUG 05 2014 000 WTPZ45 KNHC 060238 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 800 PM PDT TUE AUG 05 2014 After a decrease in the overall thunderstorm activity earlier today, a new burst of deep convection has redeveloped near the center. The outflow remains fair in all quadrants suggesting that there is little wind shear over the cyclone. Based on satellite estimates from TAFB and SAB of T3.5 on the Dvorak scale, the initial intensity is been kept at 55 knots. Given the current structure in both conventional satellite and microwave data, as well as the prevailing low shear, it is very likely that Julio will reach hurricane status within the next 6 to 12 hours. Some additional strengthening is then forecast. However, despite the expected light shear, the strengthening will be limited by the cooler ocean ahead of Julio, and the NHC forecast calls for weakening beyond 36 hours. This is consistent with the intensity models which have an upper intensity limit of 80 knots by the SHIPS model. The best estimate of the initial motion is 285 degrees at 13 knots. Julio is well embedded within the easterly flow around the periphery of the subtropical ridge. Global models keep a strong ridge to the north of the cyclone for the next 2 to 3 days, and forecast some slight erosion of the western portion of the ridge thereafter. This pattern should keep Julio on a general west-northwest track through the forecast period. Although the NHC forecast is similar to the previous one, it has been adjusted slightly northward to be consistent with the multi-model consensus TVCE and be more centered within the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 14.4N 127.5W 55 KT 65 MPH 12H 06/1200Z 14.9N 129.8W 65 KT 75 MPH 24H 07/0000Z 15.5N 133.0W 70 KT 80 MPH 36H 07/1200Z 16.3N 136.0W 75 KT 85 MPH 48H 08/0000Z 17.0N 139.0W 70 KT 80 MPH 72H 09/0000Z 18.0N 144.5W 60 KT 70 MPH 96H 10/0000Z 20.0N 149.5W 50 KT 60 MPH 120H 11/0000Z 22.0N 154.0W 45 KT 50 MPH $$ Forecaster Avila

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Tropical Storm JULIO Forecast Discussion Number 8

2014-08-05 22:54:35| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE AUG 05 2014 000 WTPZ45 KNHC 052054 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 200 PM PDT TUE AUG 05 2014 Satellite imagery this afternoon indicates that Julio is becoming better organized, with increased convective banding and cloud tops colder than -80C near the center. Satellite intensity estimates are 55 kt and 45 kt from TAFB and SAB respectively. In addition, an earlier CIMSS AMSU estimate was 53 kt. Based on these data, the initial intensity is increased to 55 kt. The initial motion is now 280/12. A low/mid-level ridge to the north of the cyclone should steer it westward to west-northwestward with some increase in forward speed during the next 3-4 days. After that, the dynamical models forecast the ridge to weaken, which would cause Julio to move more northward. The track guidance envelope is similar to the previous guidance through 72 hours, and this part of the forecast is an update of the previous forecast. From 72-120 hours, the guidance envelope has shifted significantly to the north. The new forecast track is also shifted northward, but it still lies to the south of the consensus models and all of the dynamical models except the GFDL/NAVGEM. If the current model trends continue, an additional northward adjustment may be necessary in later advisories. It should be noted that the NOAA G-IV jet is currently flying a synoptic surveillance mission for Hurricane Iselle, and the data from this mission will hopefully help the subsequent forecasts for Julio. Julio is now in a light vertical wind shear environment, and the dynamical models suggest this will continue through the forecast period. However, the forecast track takes the system over gradually decreasing sea surface temperatures during the next 48 hours. The consensus of the intensity guidance is for continued strengthening for the next 36-48 hours, and the increased banding seen during the last few hours could be the start of a faster intensification rate. The new intensity forecast continues to call for a peak intensity of 75 kt, and at this time only the HFIP-sponsored University of Wisconsin model forecasts a higher peak intensity. After 48 hours, gradual weakening is expected as the center moves along the 26C isotherm and this part of the new forecast is in best agreement with the SHIPS model. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 14.2N 126.0W 55 KT 65 MPH 12H 06/0600Z 14.7N 128.2W 60 KT 70 MPH 24H 06/1800Z 15.4N 131.4W 65 KT 75 MPH 36H 07/0600Z 16.0N 134.4W 75 KT 85 MPH 48H 07/1800Z 16.6N 137.3W 75 KT 85 MPH 72H 08/1800Z 17.5N 143.0W 70 KT 80 MPH 96H 09/1800Z 19.0N 148.5W 60 KT 70 MPH 120H 10/1800Z 21.0N 153.0W 60 KT 70 MPH $$ Forecaster Beven

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Tropical Storm BERTHA Forecast Discussion Number 20

2014-08-05 22:45:05| National Hurricane Center (Atlantic)

Issued at 500 PM EDT TUE AUG 05 2014 000 WTNT43 KNHC 052044 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 PM EDT TUE AUG 05 2014 Deep convection redeveloped over the center earlier today, but that convection was subsequently sheared off to the east-northeast. An ASCAT overpass from a few hours ago indicated that, although Bertha still had a well-defined surface circulation, the maximum winds were no more than 45 kt, Based on this, and a Dvorak classification of T3.0 from TAFB, the advisory intensity is set at 45 kt. The scatterometer data also indicated that there were no winds to tropical storm force over the western semicircle of the circulation. The SHIPS model predicts that west-southwesterly shear will increase greatly over the next day or two, and these conditions could cause more weakening than indicated by the official forecast. However, it is possible that the system may maintain more of its intensity by extracting energy from baroclinic processes associated with the frontal system just to its north. In any event, global models show the system becoming embedded within the frontal zone within 36 hours, so the official forecast indicates that the transition to a post-tropical/extratropical cyclone will be complete by that time. Bertha's heading is gradually shifting to the right and the motion is now 030/18 kt. There is little change to the track forecast philosophy. Over the next couple of days, the tropical, or post-tropical, cyclone should turn toward the northeast and accelerate ahead of an amplifying mid-level trough moving off the northeast United States coast. Later in the forecast period, the system should move swiftly east-northeastward to eastward in the mid-latitude westerlies over the North Atlantic. The track and wind radii forecast for 36 hours and beyond have been coordinated with the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 36.2N 70.3W 45 KT 50 MPH 12H 06/0600Z 38.2N 67.0W 45 KT 50 MPH 24H 06/1800Z 41.0N 61.6W 40 KT 45 MPH 36H 07/0600Z 43.7N 55.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 07/1800Z 46.0N 49.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 08/1800Z 48.0N 37.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 09/1800Z 49.0N 20.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 10/1800Z 51.0N 1.0W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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