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Tropical Storm HERMINE Forecast Discussion Number 14

2016-09-01 04:58:22| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT WED AUG 31 2016 000 WTNT44 KNHC 010258 TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 PM CDT WED AUG 31 2016 Data from NOAA and Air Force Reserve Hurricane Hunter aircraft this afternoon and evening indicate that Hermine has continued to strengthen, based on maximum 850-mb flight-level winds of 57 kt and peak SFMR surface winds of 52 kt. A recent dropsonde in the center of Hermine measured a pressure of about 998 mb, which is a decrease of 6 mb from the previous advisory. Recon fixes over the past 4 hours indicate that the estimated motion is north-northeastward or 025/09 kt. An approaching mid-tropospheric trough located over the southeastern United States and extending southward into the north-central Gulf of Mexico is expected to gradually lift out Hermine to the north-northeast tonight and Thursday, and then northeastward after 24 hours. The NHC model is in very good agreement on this developing steering flow pattern. Later in the forecast period, significant uncertainty in the track forecast remains, depending on how much the post-tropical cyclone interacts with a mid-latitude cutoff low that develops over the northeastern United States. The new NHC forecast track has been shifted slightly to the east of the previous advisory track, primarily due to the more eastward initial position determined from recent recon fixes, and lies just to the left of the consensus model TVCN. The vertical wind shear is forecast by the GFS and the ECMWF models to shift from the current west-northwesterly direction to southwesterly by 18-24 hours at about 5 to 10 kt. SSTs are expected to be near 30C. The intensity consensus IVCN again brings Hermine to hurricane strength prior to landfall and the offical forecast follows this guidance, forcing the issuance of a hurricane warning with this advisory. The predicted extratropical transition of the system is based on the global model guidance, which show the cyclone becoming embedded within a frontal zone over the eastern United States by 72 hours. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 25.8N 87.0W 50 KT 60 MPH 12H 01/1200Z 26.9N 86.4W 55 KT 65 MPH 24H 02/0000Z 28.7N 85.4W 65 KT 75 MPH 36H 02/1200Z 30.7N 83.8W 60 KT 70 MPH...INLAND 48H 03/0000Z 32.8N 81.4W 45 KT 50 MPH...INLAND 72H 04/0000Z 37.0N 76.3W 40 KT 45 MPH...POST-TROP/INLAND 96H 05/0000Z 39.0N 74.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 06/0000Z 39.0N 71.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Depression EIGHT Forecast Discussion Number 15

2016-09-01 04:44:21| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT WED AUG 31 2016 000 WTNT43 KNHC 010244 TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082016 1100 PM EDT WED AUG 31 2016 Deep convection is becoming increasingly dislocated from the center of the tropical depression because of the strong westerly vertical shear. Dvorak classifications from SAB and TAFB continue to drop as the convection becomes less organized. The initial intensity remains 25 kt. The tropical depression should not be long for this world. Last- light visible imagery suggests that the center may be becoming diffuse. The deep convection may soon either dissipate or be located far from the center. The system may shortly become entangled in a frontal boundary. If the center is no longer well defined, if there is no associated organized deep convection, or if the cyclone becomes frontal, then the system will no longer be a tropical cyclone. One or more of these options should occur within about a day, if not sooner. In about two days, the post-tropical cyclone is likely to be absorbed in a separate extratropical low. The depression is moving toward the east-northeast at about 14 kt, as it is being swept up by the southwesterlies ahead of a mid-latitude shortwave trough. The system should accelerate in the same direction until dissipation. The track is based upon the consensus of the reliable global models and is nearly the same as that from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 36.7N 70.1W 25 KT 30 MPH 12H 01/1200Z 38.2N 66.9W 30 KT 35 MPH 24H 02/0000Z 40.5N 60.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 36H 02/1200Z 43.0N 54.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 03/0000Z...DISSIPATED $$ Forecaster Landsea

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Tropical Storm HERMINE Forecast Discussion Number 13

2016-08-31 22:52:59| National Hurricane Center (Atlantic)

Issued at 400 PM CDT WED AUG 31 2016 000 WTNT44 KNHC 312052 TCDAT4 TROPICAL STORM HERMINE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 400 PM CDT WED AUG 31 2016 The system appears better organized on satellite images than it was yesterday, with more evidence of convective banding features. However, based on the NOAA Hurricane Hunter data the center is still situated near the northern edge of the main convective cloud mass. Also, data from the aircraft show a very asymmetric wind field with all of the strong winds occurring over the eastern and southeastern portions of the circulation. The advisory intensity is set to 40 kt based on SFMR-observed surface winds from the Hurricane Hunters. Hermine should be in an environment of moderate west-southwesterly shear until it nears the coast, when the dynamical models show increasing shear. The official intensity forecast has been nudged upward a bit, and there is a distinct possibility that Hermine could become a hurricane before landfall. The predicted extratropical transition of the system is based on the latest global model forecasts, which show the cyclone becoming embedded within a front over the eastern United States by 72 hours. The aircraft data show a rather broad area of light winds near the center, making the actual center fixes a little uncertain. However, the best estimate of initial motion is north-northeastward or 030/6 kt. A developing mid-level trough over the southeastern United States should cause Hermine to move north-northeastward at increasing forward speed over the next couple of days. The GFS and ECMWF global models have shifted westward from their previous predictions, and so has the new official forecast. This required a westward extension of the hurricane watch and tropical storm warning along the Florida panhandle. Later in the forecast period, there is significant uncertainty in the track of the system, which will depend on how the post-tropical cyclone interacts with a mid-tropospheric cutoff low that develops over the northeastern United States. The new official forecast keeps the cyclone closer to the east coast from 72-120 hours in deference to the latest GFS solution. It is important not to focus on the forecast landfall point of this system. In addition to the normal uncertainty in track and intensity forecasts, dangerous storm surge flooding is likely to extend along the Gulf coast well to the east and south of the path of the center. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 25.5N 87.4W 40 KT 45 MPH 12H 01/0600Z 26.5N 87.3W 45 KT 50 MPH 24H 01/1800Z 28.1N 86.3W 50 KT 60 MPH 36H 02/0600Z 30.0N 85.0W 60 KT 70 MPH 48H 02/1800Z 32.0N 82.9W 50 KT 60 MPH...INLAND 72H 03/1800Z 36.5N 77.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 04/1800Z 39.0N 74.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 05/1800Z 39.5N 72.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane LESTER Forecast Discussion Number 29

2016-08-31 22:37:22| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED AUG 31 2016 000 WTPZ43 KNHC 312037 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 29 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 200 PM PDT WED AUG 31 2016 Lester's satellite appearance has not changed much since the last advisory. Although the eye has shrunk a little it remains quite warm, and the convective ring around the eye still has tops colder than -70C. The initial intensity remains 115 kt based on the latest Dvorak estimates from TAFB and SAB, and the UW-CIMSS ADT. Lester has some annular characteristics, with little convective banding. Given the forecast track through a region of SSTs of 26-27C and in low shear, steady weakening is expected through the forecast period. Given the annular structure, the NHC forecast remains above most of the guidance through much of the forecast period. The initial motion estimate is 275/11. The track forecast reasoning remains unchanged, as Lester will continue to be steered westward and then turn west-northwestward by a mid-level ridge centered north of the Hawaiian Islands through the forecast period. The track models remain in generally good agreement on this scenario, but there remains some significant across-track spread in the guidance near the Hawaiian Islands. The GFS and UKMET models are along the southern edge of the main guidance envelope, with a track near or over the islands, while the HWRF, GFDL, and COAMPS-TC are farther north. The NHC forecast is largely an update of the previous one, and lies very close to the multi-model consensus through the period. All interests in the Hawaiian Islands should continue to monitor the progress of Lester, as it is too early to determine what impacts there could be along the island chain given the track forecast uncertainty in the 3 to 5 day period. The NASA Gulfstream-V jet is flying a synoptic surveillance mission around Lester to acquire additional data for tonight's 00Z global model cycle. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 18.0N 139.9W 115 KT 130 MPH 12H 01/0600Z 18.2N 141.6W 105 KT 120 MPH 24H 01/1800Z 18.6N 143.9W 100 KT 115 MPH 36H 02/0600Z 19.2N 146.3W 90 KT 105 MPH 48H 02/1800Z 19.8N 149.0W 80 KT 90 MPH 72H 03/1800Z 21.4N 154.4W 70 KT 80 MPH 96H 04/1800Z 23.2N 159.5W 60 KT 70 MPH 120H 05/1800Z 25.0N 164.0W 50 KT 60 MPH $$ Forecaster Brennan

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Tropical Depression EIGHT Forecast Discussion Number 14

2016-08-31 22:35:50| National Hurricane Center (Atlantic)

Issued at 500 PM EDT WED AUG 31 2016 000 WTNT43 KNHC 312035 TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082016 500 PM EDT WED AUG 31 2016 This depression has been a challenging cyclone. After the earlier apparent improvement in the cloud pattern, recent satellite images indicate the system has actually become less organized. While there is a broken band in the eastern semicircle, the depression looks elongated, with a less well-defined center. The initial wind speed is reduced to 25 kt on this advisory, which is backed up by ASCAT data of 20 to 25 kt. I'm beginning to think that the long-forecast intensification is not going to occur with this depression. Other than persistence, this idea is supported by the higher shear values in the recent SHIPS and global model guidance. While I'm not ready to totally abandon any strengthening, the new NHC forecast is reduced 5 to 10 kt from the previous one and is below the model consensus. The cyclone should become extratropical within 2 days, and be absorbed within a larger frontal zone in 3 days. An alternative, but realistic, scenario, is that the cyclone becomes a remnant low tomorrow due to marginal environmental conditions causing a lack of organized deep convection. The cyclone is moving northeastward at about 14 kt. It should continue to accelerate to the northeast within the southwesterly flow ahead of an amplifying mid-latitude trough. No significant change to the previous forecast was made. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 36.3N 71.9W 25 KT 30 MPH 12H 01/0600Z 37.7N 69.3W 30 KT 35 MPH 24H 01/1800Z 39.9N 64.0W 35 KT 40 MPH 36H 02/0600Z 42.0N 57.5W 35 KT 40 MPH...POST-TROPICAL 48H 02/1800Z 44.0N 51.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 03/1800Z...DISSIPATED $$ Forecaster Blake

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