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Hurricane ISELLE Forecast Discussion Number 21

2014-08-05 16:53:40| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE AUG 05 2014 000 WTPZ44 KNHC 051453 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT TUE AUG 05 2014 Iselle has changed little in organization during the past six hours. The eye remains well defined, with cloud tops to -70C occurring in the eyewall. Analyses from the SHIPS model and from CIMSS at the University of Wisconsin indicate 15-20 kt of southwesterly vertical wind shear over the system. However, this has not yet disrupted the inner core. The initial intensity remains 110 kt based on a combination of subjective and objective satellite intensity estimates. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Iselle near 06/0600Z, which will provide ground truth for the intensity. The initial motion estimate is 270/8 kt. The subtropical ridge to the north of Iselle should strengthen during the next several days, which should steer the cyclone generally west-northwestward with an increase in forward speed. The track model guidance remains tightly clustered and forecasts Iselle to pass near or over the Hawaiian Islands in 72-84 hours. Based on this, the new forecast track is again just an update of the previous track, and it lies in the center of the track guidance envelope. The analyzed and 24-hour forecast shear have both increased since the previous advisory, and it is likely that Iselle will lose its annular structure later today or tonight. This should result in weakening along the lines of the previous forecast since a significant part of the circulation is over sea surface temperatures of less than 26C. The intensity forecast becomes more uncertain after 36 hours. The cyclone will be moving over increasing sea surface temperatures west of 152W. The dynamical models are in poor agreement on how much shear the Iselle will experience, with the UKMET forecasting strong shear while the GFS/ECMWF forecast less shear. One last factor is that the cyclone is likely to encounter a very dry air mass as it approaches Hawaii. The intensity guidance responds to these factors by diverging. The SHIPS and Florida State Superensemble forecast an intensity near 40 kt when Iselle gets near Hawaii, while the GFDL and HWRF forecast it to be a hurricane. The intensity forecast from 48-120 hours has been nudged upward in agreement with the LGEM model and the intensity consensus, and it calls for Iselle to be just below hurricane strength near Hawaii. Interests in the Hawaiian Islands should closely monitor the progress of Iselle. However, it is important not to focus too closely on the exact track and intensity forecasts because the average track error 72 hours out is about 100 miles, the average intensity error is about 15 kt. In addition, the hazards of a tropical cyclone can extend over a broad area well away from the center. This is the last advisory issued by the National Hurricane Center on Iselle. Future Public Advisories will be issued by the Central Pacific Hurricane Center under AWIPS header HFOTCPCP3 and WMO header WTPA33 PHFO, while Forecast/Advisories will be issued under AWIPS header HFOTCMCP3 and WMO header WTPA23 PHFO. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.0N 139.5W 110 KT 125 MPH 12H 06/0000Z 16.3N 141.1W 100 KT 115 MPH 24H 06/1200Z 16.9N 143.9W 85 KT 100 MPH 36H 07/0000Z 17.6N 147.2W 70 KT 80 MPH 48H 07/1200Z 18.3N 150.4W 65 KT 75 MPH 72H 08/1200Z 20.0N 156.5W 55 KT 65 MPH...NEAR HAWAII 96H 09/1200Z 21.0N 162.0W 45 KT 50 MPH 120H 10/1200Z 21.5N 166.5W 35 KT 40 MPH $$ Forecaster Beven

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Tropical Storm JULIO Forecast Discussion Number 7

2014-08-05 16:34:59| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE AUG 05 2014 000 WTPZ45 KNHC 051434 TCDEP5 TROPICAL STORM JULIO DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102014 800 AM PDT TUE AUG 05 2014 Microwave imagery indicates that the center of Julio is located on the northern edge of the convective canopy, consistent with 10 kt or so of northeasterly shear analyzed over the cyclone by UW-CIMSS satellite analyses and the SHIPS model. The initial intensity remains 50 kt based on a blend of the latest Dvorak classifications from TAFB and SAB. Conditions should support gradual strengthening during the next 2 to 3 days, and the NHC forecast shows Julio becoming a hurricane in about 24 hours. By day 4, the cyclone will be moving over more marginal SSTs around 26C, but then back over warmer water by day 5. Given that the shear remains relatively low late in the period, only a little weakening is shown by day 4 with the intensity leveling off afterward. The NHC forecast is a little above the IVCN intensity consensus through the period. Microwave and geostationary satellite fixes suggest that the center is located a little to the north of previous estimates, providing an initial motion estimate of 275/11. The track forecast reasoning remains unchanged, as Julio will be steered generally westward through 96 hours by a mid-level ridge to the north. By day 5, the cyclone will be approaching the western edge of the ridge, which should result in a turn toward the west-northwest. The combination of the more northward initial position and a northward shift in the guidance results in the NHC track forecast being nudged northward a bit. The official forecast close to a blend of the ECMWF and GFS models on the south side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 14.0N 124.7W 50 KT 60 MPH 12H 06/0000Z 14.4N 126.8W 55 KT 65 MPH 24H 06/1200Z 15.1N 129.8W 65 KT 75 MPH 36H 07/0000Z 15.7N 132.8W 75 KT 85 MPH 48H 07/1200Z 16.1N 135.7W 75 KT 85 MPH 72H 08/1200Z 17.0N 141.5W 75 KT 85 MPH 96H 09/1200Z 18.0N 147.0W 65 KT 75 MPH 120H 10/1200Z 20.0N 152.5W 65 KT 75 MPH $$ Forecaster Brennan

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Tropical Storm BERTHA Forecast Discussion Number 19

2014-08-05 16:34:01| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT TUE AUG 05 2014 000 WTNT43 KNHC 051433 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 AM EDT TUE AUG 05 2014 Increasing westerly vertical shear is displacing deep convection to the east of the low-level center of Bertha, which is clearly exposed in visible satellite images. The current intensity is adjusted down a bit in accordance with observations from a NOAA Hurricane Hunter plane a few hours ago. Since the shear is forecast to become even stronger over the next couple of days, additional weakening would be expected due to those conditions. However, the cyclone might be able to draw energy from baroclinic process associated with a frontal zone not far to its north, and maintain at least some of its intensity. The system is forecast to merge with that front and become an extratropical cyclone within 36 hours. It is also possible, however, that the shear will become so strong that Bertha would be reduced to a convection-free post-tropical cyclone before extratropical transition takes place. The NOAA Ocean Prediction Center has provided input to the official intensity forecast. Bertha continues moving north-northeastward near 19 kt. The tropical, or post-tropical, cyclone is forecast to accelerate northeastward ahead of an amplifying mid-level trough near the United States east coast during the next couple of days. Thereafter, the system should move quickly east-northeastward to eastward in the mid-latitude westerlies over the North Atlantic. The track forecast for 36 hours and beyond is also based on input from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 34.8N 71.9W 50 KT 60 MPH 12H 06/0000Z 37.1N 69.2W 50 KT 60 MPH 24H 06/1200Z 39.8N 64.5W 50 KT 60 MPH 36H 07/0000Z 42.5N 59.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 07/1200Z 45.0N 53.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 08/1200Z 49.0N 40.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 09/1200Z 49.0N 22.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 10/1200Z 51.0N 2.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Storm BERTHA Forecast Discussion Number 18

2014-08-05 10:59:32| National Hurricane Center (Atlantic)

Issued at 500 AM EDT TUE AUG 05 2014 000 WTNT43 KNHC 050859 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 AM EDT TUE AUG 05 2014 Data from an Air Force Reserve reconnaissance aircraft indicate that Bertha's winds have decreased below hurricane strength, which is logical given that little deep convection now exists near the center. The initial intensity has been lowered to 55 kt, which could generous given that only 45-kt surface winds have been reported thus far. However, the recon aircraft has not yet completed its entire mission, so I do not want to bring the intensity too quickly in the event stronger winds are found east of the center and/or deep convection redevelops. The initial motion estimate is an uncertain 015/19 kt. Bertha briefly accelerated to about 21-22 kt after losing its deep convection a few hours ago, but recon fix data suggests that the cyclone's motion has settled down to around 19 kt now. Overall, the official track forecast and philosophy remains basically unchanged. The NHC model guidance remains in very good agreement on Bertha continuing its northeastward trek around the western periphery of a deep-layer subtropical ridge for the next 24 hours or so, and then accelerate eastward after getting caught up in the mid-latitude westerlies by 36-48 hours. The official forecast track is similar to but slightly west of the previous advisory track to account for the more westward initial position, and closely follows the consensus model TVCA. Bertha is forecast to experience increasing vertical wind shear over the next two days, with the shear reaching 50 kt or more by 24-36 hours. The combination of the strong shear and decreasing SSTs should induce steady weakening and cause extratropical transition by 36 hours or so. However, not as much weakening is expected with such strong shear conditions due to the expected infusion of baroclinic energy associated with a strong mid-latitude trough that is forecast to capture Bertha by 48 hours, which will help maintain the cyclone's intensity. The intensity forecast during the extratropical phase closely follows input from the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 33.4N 72.9W 55 KT 65 MPH 12H 05/1800Z 35.9N 70.8W 55 KT 65 MPH 24H 06/0600Z 38.6N 66.9W 50 KT 60 MPH 36H 06/1800Z 41.3N 62.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 07/0600Z 44.1N 56.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 08/0600Z 48.5N 44.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 09/0600Z 49.3N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 10/0600Z 50.3N 14.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane ISELLE Forecast Discussion Number 20

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

Issued at 200 AM PDT TUE AUG 05 2014 000 WTPZ44 KNHC 050855 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 AM PDT TUE AUG 05 2014 Although Iselle's eye remain large and distinct, cloud tops have been warming significantly since the previous advisory. Also, some westerly shear is beginning to impinge on the cyclone, and the CDO has become elongated a little in a northeast-southwest orientation. The aforementioned observations all suggest weakening, and this is noted by a decrease in the Dvorak T-numbers from TAFB and SAB. The initial intensity is, therefore, lowered to 110 kt for this advisory, which is a blend of subjective and objective satellite intensity estimates. The initial motion estimate is 270/07 kt. After a slight jog to the west-southwest, Iselle appears to have returned to a due west course. The NHC model guidance remains tightly clustered and in excellent agreement on Iselle moving slowly westward for another 12-24 hours, and then turning more west-northwestward at a faster forward speed as the ridge to its north gradually strengthens. The new NHC forecast track is just an update of the previous advisory track, and is close to the very reliable consensus model, TVCA. On the forecast track, the center of Iselle should move near or over portions of the Hawaiian Islands in 72-84 hours. Since Iselle is an annular hurricane, only slow weakening is forecast, especially since the vertical shear is forecast to remain 5 kt or less for the next 72 hours or so. The GFS-based SHIPS model is showing more significant weakening and makes Iselle a tropical storm in 36 hours, which seems premature. This is due in part to the SSTs being about 0.5 degree cooler in the model than what is currently observed along the cyclone's path. The official intensity forecast follows the consensus model, ICON, but is slightly higher to account for the low bias of the SHIPS model. Remnant low status is expected by Day 5. Interests in the Hawaiian Islands should closely monitor the progress of Iselle. However, it is important not to focus too closely on the exact track and intensity forecasts because the average track error 72 hours out is about 100 miles, the average intensity error is about 15 kt, and because the hazards of a tropical cyclone can extend over a broad area often well away from the center. Iselle is expected to cross into the Central Pacific Hurricane Center's area of responsibility around 1800 UTC today. Once this occurs, the Central Pacific Hurricane Center in Honolulu, Hawaii, will begin issuing advisories on Iselle. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 15.9N 138.6W 110 KT 125 MPH 12H 05/1800Z 16.2N 140.1W 100 KT 115 MPH 24H 06/0600Z 16.7N 142.7W 85 KT 100 MPH 36H 06/1800Z 17.3N 145.8W 70 KT 80 MPH 48H 07/0600Z 18.1N 149.2W 60 KT 70 MPH 72H 08/0600Z 19.7N 155.6W 50 KT 60 MPH 96H 09/0600Z 21.1N 161.4W 40 KT 45 MPH 120H 10/0600Z 21.8N 166.3W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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