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Tropical Depression TWELVE Forecast Discussion Number 1

2016-09-14 16:42:29| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED SEP 14 2016 000 WTNT42 KNHC 141442 TCDAT2 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST WED SEP 14 2016 Satellite imagery, scatterometer data, and surface observations indicate that the low pressure area over the Cabo Verde Islands has developed a well-defined circulation and sufficient organized convection to be considered a tropical depression. The initial intensity is set at 30 kt based on the scatterometer data along with satellite intensity estimates from TAFB and SAB. The initial motion is 300/12. A low- to mid-level ridge should steer the system west-northwestward and then westward during the forecast period, with some decrease in forward speed after 36 hours as the ridge weakens slightly. The forecast track is near the center of the guidance envelope and close to the various consensus models. Some strengthening is expected during the next 12-24 hours. After that, the cyclone is likely to encounter strong westerly vertical wind shear while over sea surface temperatures of about 26C. This combination should lead to weakening, and the intensity forecast shows the system weakening back to a depression by 36 hours. Near the end of the forecast period, the dynamical models diverge on the evolution of the upper-level winds, with the ECMWF and UKMET forecasting a more favorable pattern than the GFS. Based on this, the forecast shows some re-intensification by 120 hours. An alternative scenario is that the cyclone degenerates to a tropical wave as forecast by the GFS. Overall, the intensity forecast is on the low side of the guidance in best agreement with the LGEM. Locally heavy rains and gusty winds are possible over the Cabo Verde Islands. However, current indications are that the cyclone will not reach tropical-storm strength until it has moved west of the islands. Therefore, watches and warnings are not required at this time. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 17.0N 25.0W 30 KT 35 MPH 12H 15/0000Z 17.5N 26.8W 35 KT 40 MPH 24H 15/1200Z 17.9N 29.3W 35 KT 40 MPH 36H 16/0000Z 17.9N 31.7W 30 KT 35 MPH 48H 16/1200Z 17.8N 34.0W 30 KT 35 MPH 72H 17/1200Z 17.5N 38.0W 30 KT 35 MPH 96H 18/1200Z 17.5N 41.5W 35 KT 40 MPH 120H 19/1200Z 18.0N 45.5W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm JULIA Forecast Discussion Number 2

2016-09-14 10:47:22| National Hurricane Center (Atlantic)

Issued at 500 AM EDT WED SEP 14 2016 000 WTNT41 KNHC 140847 TCDAT1 TROPICAL STORM JULIA DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112016 500 AM EDT WED SEP 14 2016 Julia continues to produce bands of showers and thunderstorms primarily over water to the northeast of its center, but this activity has become a little more separated from the center overnight. The strong winds that occurred during the evening along the northeast Florida coast have spread northward along the coast of southern Georgia with recent surface observations reporting wind gusts to tropical storm force. Julia should gradually weaken during the next day or so due to continued land interaction and westerly shear. The updated intensity forecast calls for Julia to weaken to a tropical depression later today and become a remnant low on Thursday. This is supported by the global models, which show the low filling and wind field gradually diminishing over the next 36 hours. Julia is moving northward at about 6 kt. The tropical cyclone is forecast to slow down later today, and drift northward over eastern Georgia during the next couple of days. The track guidance has shifted eastward this cycle, and the official forecast has been adjusted accordingly. The slow forward speed of Julia is expected to result in locally heavy rainfall of 3 to 6 inches with isolated maximum amounts near 10 inches along the Georgia and South Carolina coastlines. These rains could result in flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 30.9N 81.8W 35 KT 40 MPH...INLAND 12H 14/1800Z 31.6N 81.8W 30 KT 35 MPH...INLAND 24H 15/0600Z 31.9N 81.8W 25 KT 30 MPH...INLAND 36H 15/1800Z 32.1N 81.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 16/0600Z 32.2N 81.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 17/0600Z...DISSIPATED $$ Forecaster Brown

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Hurricane ORLENE Forecast Discussion Number 14

2016-09-14 10:41:22| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED SEP 14 2016 000 WTPZ41 KNHC 140841 TCDEP1 HURRICANE ORLENE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 AM PDT WED SEP 14 2016 There has been little change in the structure of Orlene overnight. Recent microwave data indicate that the center is a little farther south than previously estimated, and it is located near the southern portion of the small central dense overcast. A blend of the latest Dvorak T- and CI-numbers results in an initial wind speed estimate of 70 kt for this advisory. Vertical shear over Orlene is forecast to decrease today and remain very low during the next several days, however, the tropical cyclone is forecast to be over marginally warm SSTs and move into a drier and more stable air mass. These environmental conditions are expected to result in gradual weakening of Orlene during the next several days. The new NHC intensity forecast is slightly lower than the previous advisory during the first 24 hours, but is unchanged thereafter and is in good agreement with the IVCN intensity model consensus. Orlene has become nearly stationary overnight as it is located within a break in the subtropical ridge. The ridge is forecast to re-strengthen during the next couple of days, which should produce a west or west-southwestward motion at a faster forward speed. Late in the forecast period, a large mid- to upper-level low expected to be well northeast of the Hawaiian Islands should produce a break in the subtropical ridge, allowing the cyclone to turn west-northwestward. The track guidance is in much better agreement than a day ago, and the updated NHC forecast is near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 20.2N 118.8W 70 KT 80 MPH 12H 14/1800Z 20.2N 119.3W 60 KT 70 MPH 24H 15/0600Z 20.0N 120.7W 55 KT 65 MPH 36H 15/1800Z 19.9N 122.6W 50 KT 60 MPH 48H 16/0600Z 19.8N 124.8W 45 KT 50 MPH 72H 17/0600Z 19.8N 129.7W 40 KT 45 MPH 96H 18/0600Z 20.1N 134.7W 35 KT 40 MPH 120H 19/0600Z 21.5N 138.7W 30 KT 35 MPH $$ Forecaster Brown

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Tropical Storm IAN Forecast Discussion Number 8

2016-09-14 10:37:21| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED SEP 14 2016 000 WTNT45 KNHC 140837 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 AM AST WED SEP 14 2016 The cloud pattern of Ian has changed little during the past several hours. The low-level center of the tropical storm is completely exposed and located more than 100 n mi south of the main area of deep convection. This poor structure is the result of about 30 kt of south-southwesterly vertical wind shear. The initial intensity is held at 45 kt, in agreement with the earlier scatterometer data and a Dvorak CI-number from TAFB. Ian is moving northward at about 13 kt, and is being steered by the southerly flow between a mid- to upper-level low to its west and a ridge to its east. A northward to north-northeastward motion at about the same forward speed is forecast during the next 24 hours as the steering pattern more or less persists. After that time, a shortwave trough is expected to move east of Atlantic Canada, and that should cause Ian to turn northeastward and sharply accelerate until the cyclone becomes absorbed by a large extratropical low in 3 to 4 days. The models are in good agreement, and the official forecast lies closest to a consensus of the GFS and ECMWF models. The strong shear that has been affecting Ian since genesis is expected to let up some during the next 24 to 36 hours. The predicted lower shear, fairly warm water, and baroclinic forcing should allow Ian to strengthen a little during the next day or two. Beyond a couple of days, Ian is forecast to move over sharply cooler sea surface temperatures and into an environment of strong shear. These conditions should cause the cyclone to lose its tropical characteristics in 2 to 3 days. The NHC intensity forecast is an update of the previous one, and lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 29.3N 53.0W 45 KT 50 MPH 12H 14/1800Z 31.3N 53.2W 50 KT 60 MPH 24H 15/0600Z 34.0N 52.3W 50 KT 60 MPH 36H 15/1800Z 37.2N 49.2W 55 KT 65 MPH 48H 16/0600Z 41.6N 43.6W 55 KT 65 MPH 72H 17/0600Z 53.4N 28.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 18/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm IAN Forecast Discussion Number 7

2016-09-14 05:54:50| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE SEP 13 2016 000 WTNT45 KNHC 140354 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 PM AST TUE SEP 13 2016 Ian's cloud pattern has changed little in organization since this afternoon. The low-level center remains exposed to the south of a fan-shaped mass of deep convection. This structure is consistent with a deep-layer southwesterly vertical shear of nearly 40 kt associated with a mid- to upper-tropospheric cyclone to the west of the cyclone. A 0018Z ASCAT pass showed reliable surface winds near 45 kt well north of the center, which agrees with a TAFB satellite classifciation of T3.0. On this basis, the initial intensity is increased to 45 kt. The initial motion estimate has been nudged a little more to the right than earlier today and is now 345/11 kt. Ian should continue to move generally northward into a weakness in the subtropical ridge over the central Atlantic during the next 24 hours or so. A significant acceleration toward the northeast should occur in about 36 hours when a shortwave trough moving through Atlantic Canada approaches Ian. The NHC track forecast is adjusted to the right of the previous one, especially after 24 hours, and is in agreement with the the latest track consensus aids. The SHIPS output indicates that the shear should decrease, beginning in about 12 hours, roughly around the time that Ian becomes co-located with the upper low to its west. The shear is forecast to reach a relative minimum 24 hours later while the flow aloft gradually becomes more diffluent. This baroclinic forcing is expected to result in some intensification while Ian remains over warm waters, though the cyclone could possess attributes of both a tropical and an extratropical cyclone. Extratropical transition is indicated in 2 to 3 days, with absorption by a larger extratropical storm system over the North Atlantic likely around 72 hours. The NHC intensity forecast is about the same as the previous one and near the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 27.6N 52.8W 45 KT 50 MPH 12H 14/1200Z 29.8N 53.2W 45 KT 50 MPH 24H 15/0000Z 32.3N 53.1W 50 KT 60 MPH 36H 15/1200Z 35.2N 51.3W 55 KT 65 MPH 48H 16/0000Z 39.4N 47.0W 55 KT 65 MPH 72H 17/0000Z 49.7N 33.7W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 18/0000Z...ABSORBED $$ Forecaster Kimberlain

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