Home › discussion
 

Keywords :   


Tag: discussion

Tropical Depression TWELVE Forecast Discussion Number 5

2016-09-15 16:36:58| National Hurricane Center (Atlantic)

Issued at 1100 AM AST THU SEP 15 2016 ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST THU SEP 15 2016 Visible satellite images indicate that the depression has a rather impressive low-level circulation, although all the deep convection is far removed from the center due to southwesterly shear. Given such a well-defined circulation, the depression could have become a tropical storm overnight. The initial wind speed, however, remains 30 kt using a blend of the TAFB/SAB estimates with any of the more reliable ASCAT passes unfortunately missing the center during the past 18 hours. An upper-level trough to the northwest of the cyclone is expected to cause an increase in shear during the next day or so, which will likely cause the cyclone to weaken. Beyond 48 hours, most of the models show the shear relaxing, with an upper-level high taking the place of the trough, and the cyclone is forecast to move over warmer waters. This will probably promote a restrengthening trend, although guidance is in poor agreement on how much the winds could increase. Thus, the official forecast is reduced a little bit for Friday/Saturday due to the shear, then is the same as the previous one, showing a slow restrengthening early next week. It is also possible the cyclone will degenerate into a remnant low for a while due to the shear, although this isn't the likeliest scenario. The depression is moving westward at about 11 kt, and this general motion should continue for a day or so while it moves around the Atlantic subtropical ridge. This ridge is forecast by much of the guidance to strengthen and build westward, which would force the depression to the west-southwest over the weekend. Early next week, the cyclone could begin to gain some latitude as it reaches the southwestern periphery of the ridge. Guidance is in good agreement on this scenario, except for the GFDL which appears to be a northward outlier. The official forecast track is very close to a blend of the other models in the TVCN consensus minus the GFDL, and is basically an update of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 17.7N 30.4W 30 KT 35 MPH 12H 16/0000Z 17.8N 32.2W 30 KT 35 MPH 24H 16/1200Z 17.9N 34.8W 30 KT 35 MPH 36H 17/0000Z 17.7N 37.4W 25 KT 30 MPH 48H 17/1200Z 17.4N 40.1W 25 KT 30 MPH 72H 18/1200Z 16.5N 45.2W 30 KT 35 MPH 96H 19/1200Z 16.7N 50.3W 35 KT 40 MPH 120H 20/1200Z 17.5N 55.0W 40 KT 45 MPH $$ Forecaster Blake NNNN

Tags: number discussion twelve tropical

 

Tropical Depression JULIA Forecast Discussion Number 6

2016-09-15 10:40:56| National Hurricane Center (Atlantic)

Issued at 500 AM EDT THU SEP 15 2016 000 WTNT41 KNHC 150840 TCDAT1 TROPICAL DEPRESSION JULIA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112016 500 AM EDT THU SEP 15 2016 Westerly shear of about 25 knots has advected dry air over Julia and removed all of the deep convection from the cyclone center, with the coldest cloud tops now more than 100 n mi to the east. Coastal observations have shown the winds decreasing overnight, with most locations now reporting sustained winds of 20 to 25 kt. Based on these data, Julia is downgraded to a depression with an initial intensity of 30 kt, which is in agreement with a blend of the latest Dvorak Final-T and CI numbers from TAFB and SAB. Despite the cyclone being situated over warm SSTs, persistent shear and dry air should result in little change in intensity during the next few days. Remnant low status is forecast at 72 hours, but this could occur much sooner if organized deep convection does not return. The remnant low is forecast to dissipate in 4-5 days, consistent with the latest GFS and ECMWF solutions. Julia has moved little overnight, and the initial motion estimate is a slow eastward drift at 2 kt. The shallow cyclone is expected to continue drifting eastward today and then meander in weak steering currents until dissipation. This forecast is based on the latest GFS and ECMWF tracks and is similar to the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 32.0N 79.6W 30 KT 35 MPH 12H 15/1800Z 32.0N 79.3W 30 KT 35 MPH 24H 16/0600Z 32.0N 78.9W 30 KT 35 MPH 36H 16/1800Z 32.0N 78.9W 30 KT 35 MPH 48H 17/0600Z 31.9N 79.0W 30 KT 35 MPH 72H 18/0600Z 31.9N 79.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 19/0600Z 32.0N 79.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 20/0600Z...DISSIPATED $$ Forecaster Brennan

Tags: number discussion tropical depression

 
 

Tropical Storm IAN Forecast Discussion Number 12

2016-09-15 10:36:06| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 15 2016 000 WTNT45 KNHC 150835 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 AM AST THU SEP 15 2016 Ian continues to have a structure somewhat resembling a subtropical cyclone, with the low-level center situated beneath an upper-level low and a cloud pattern featuring a broken band of convection. However, there is still some moderate to deep convection not too far from the center, and the most recent AMSU pass still showed a deep warm core structure. The initial intensity remains 45 kt in agreement with the latest satellite classification of ST3.5 from TAFB. Ian is running out of time to strengthen via diabatic processes, and most of the strengthening shown here is expected to be due to baroclinic effects, especially given the current convective structure. By 24 hours, strong shear and cool SSTs should result in Ian being post-tropical, and the cyclone should be fully extratropical by 36 hours. The intensity forecast is based mainly on the global models and guidance from the Ocean Prediction Center, and shows the post-tropical cyclone intensifying to near hurricane strength before it's absorbed by a larger extratropical low in 48 hours. The initial motion estimate is 025/17. Ian should accelerate northeastward ahead of a large upper-level trough moving eastward across the northwestern Atlantic during the next 36 hours before being absorbed. The new NHC track forecast is similar to the previous one and near the middle of the guidance envelope. The initial 34-kt wind radii were adjusted based on a partial ASCAT pass from around 0100 UTC. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 35.5N 52.4W 45 KT 50 MPH 12H 15/1800Z 38.3N 49.8W 50 KT 60 MPH 24H 16/0600Z 43.0N 43.7W 55 KT 65 MPH...POST-TROPICAL 36H 16/1800Z 49.1N 35.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 17/0600Z...ABSORBED BY ANOTHER EXTRATROPICAL LOW $$ Forecaster Brennan

Tags: number discussion storm ian

 

Tropical Depression TWELVE Forecast Discussion Number 4

2016-09-15 10:32:58| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 15 2016 000 WTNT42 KNHC 150832 TCDAT2 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST THU SEP 15 2016 AMSR2 microwave data from a few hours ago indicated that the depression's center was about a degree west of the deep convection due to 20 kt of westerly shear. Since the cyclone's structure has not improved, and subjective Dvorak estimates have not changed from six hours ago, the initial intensity remains 30 kt. The westerly shear is expected to increase during the next 24 hours, and with a relatively drier air mass surrounding the cyclone, any strengthening during the next couple of days now appears less likely. After 48 hours, the shear is forecast to relax to some degree, but the global models disagree on exactly how much. Nonetheless, if the depression can survive the next couple of days, the environment should improve enough to allow for some strengthening by the end of the forecast period. The new NHC intensity forecast now holds the cyclone as a 30-kt depression for the next 3 days, followed by slight strengthening on days 4 and 5. This forecast is in best agreement with the statistical-dynamical SHIPS and LGEM models. The microwave data indicate that the depression has been moving a little faster toward the west at 275/14 kt. The Bermuda-Azores high is expected to steer the depression generally westward across the tropical Atlantic during the entire 5-day forecast period. A south-of-due-west motion is even possible on days 2 and 3, especially if the cyclone remains weak. With the exception of the GFDL, which shows more strengthening and is an outlier way to the north of the other models, the guidance envelope is relatively tight. To account for the apparent north bias of the GFDL, the updated NHC track forecast is a bit south of the TVCN multi-model consensus. The new forecast is also a little faster than and south of the previous forecast, especially on days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 17.6N 29.3W 30 KT 35 MPH 12H 15/1800Z 17.8N 31.2W 30 KT 35 MPH 24H 16/0600Z 18.0N 33.7W 30 KT 35 MPH 36H 16/1800Z 17.9N 36.4W 30 KT 35 MPH 48H 17/0600Z 17.6N 39.0W 30 KT 35 MPH 72H 18/0600Z 16.7N 43.8W 30 KT 35 MPH 96H 19/0600Z 16.5N 49.0W 35 KT 40 MPH 120H 20/0600Z 17.0N 53.5W 40 KT 45 MPH $$ Forecaster Berg

Tags: number discussion twelve tropical

 

Tropical Storm IAN Forecast Discussion Number 11

2016-09-15 04:56:57| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED SEP 14 2016 000 WTNT45 KNHC 150256 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 PM AST WED SEP 14 2016 Water vapor imagery indicates that an upper-level low has moved over and has become superimposed with Ian's low-level center. Broken convective banding features, along with an abundance of lightning, have developed northwest through northeast of the center. Drifting buoy 41506, located about 20 nmi north of the center reported 1001.5 mb pressure at 0100Z. Another drifting buoy located about 150 nmi east of the center reported a pressure of around 1015 mb, and the pressure difference between Ian and that buoy supports a gradient wind of 50-52 kt. For now, the initial intensity of Ian will remain at 45 kt since another scatterometer pass over the cyclone is due shortly. Ship BATFR13 has been reporting winds of 30 kt about 250 nmi north-northeast of the center, which supports the previous and current 34-kt wind radius of 200 nmi in that quadrant. Ian has made the much anticipated turn toward the north-northeast, and the cyclone is now moving 015/12 kt. Ian should gradually turn more toward the northeast during the next 24 hours and accelerate as the storm moves around the western portion of Bermuda-Azores High, and ahead of an advancing strong shortwave trough. The new forecast track is essentially just an extension of the previous advisory track and lies down the middle of the tightly packed NHC track model guidance. Ian is looking more like a subtropical cyclone on conventional satellite. However, the recent increase in deep convection near and within 75 nmi of the center, along with recent AMSU data indicating that the system still has a mid- to upper-level warm-core structure, support maintaining Ian as a tropical cyclone. Ian has about 24 hours or so remaining to intensify as a tropical cyclone while it is located south of the Gulf Stream and over warm waters. By 36 hours, Ian will lose its tropical characteristics over cooler water, but some baroclinic forcing is expected to help strengthen the cyclone. By 72 hours, Ian is expected to be absorbed by a larger extratropical low. The intensity forecast remains unchanged from the previous advisory and follows the trend of global models. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 33.9N 53.4W 45 KT 50 MPH 12H 15/1200Z 36.3N 51.6W 50 KT 60 MPH 24H 16/0000Z 40.3N 47.0W 50 KT 60 MPH 36H 16/1200Z 45.8N 39.7W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 17/0000Z 51.7N 32.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 18/0000Z...ABSORBED $$ Forecaster Stewart

Tags: number discussion storm ian

 

Sites : [815] [816] [817] [818] [819] [820] [821] [822] [823] [824] [825] [826] [827] [828] [829] [830] [831] [832] [833] [834] next »