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Tropical Storm KEVIN Forecast Discussion Number 13

2015-09-03 22:45:18| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU SEP 03 2015 000 WTPZ44 KNHC 032044 TCDEP4 TROPICAL STORM KEVIN DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142015 200 PM PDT THU SEP 03 2015 The intensity and coverage of deep convection being produced by Kevin has been decreasing, although this may be a diurnal fluctuation. There are some ill-defined banding features over the northern semicircle, and the cyclone still has some outflow over the southern part of the circulation. The latter is a bit surprising, given the south-southwesterly shear over the system. The current intensity is held at 45 kt which is consistent with the latest Dvorak estimate from TAFB. There is a narrow window of opportunity for intensification in the short term, i.e. during the next 12 to 24 hours. Thereafter, the shear is forecast to increase and the cyclone should be ingesting drier and more stable air. The official forecast shows slight strengthening overnight followed by weakening and eventual degeneration into a remnant low in about 3 days. This is very close to the latest model consensus. Some of the guidance, such as the SHIPS model, show an even faster weakening than indicated here. Recent microwave imagery has provided some good center fixes, and the initial motion is a slightly faster 360/7. Kevin should move northward to northwestward on the southwest side of a mid-level subtropical anticyclone for the next day or two. Afterward, the weakening and increasingly shallow cyclone is likely to turn toward the west and be steered mainly by the low-level flow. The GFDL and HWRF models show a much more northward track, and appear to be unrealistic. The official track forecast is similar to the previous one, and close to the latest ECMWF solution. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 18.7N 115.8W 45 KT 50 MPH 12H 04/0600Z 19.8N 115.8W 50 KT 60 MPH 24H 04/1800Z 21.2N 115.8W 50 KT 60 MPH 36H 05/0600Z 22.0N 116.3W 45 KT 50 MPH 48H 05/1800Z 22.3N 117.1W 40 KT 45 MPH 72H 06/1800Z 22.5N 119.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 07/1800Z 22.5N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm FRED Forecast Discussion Number 20

2015-09-03 22:33:29| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU SEP 03 2015 000 WTNT41 KNHC 032033 TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 500 PM AST THU SEP 03 2015 Despite the 35-kt westerly wind shear impinging on Fred, deep convection, once again, regenerated near or over the center of the vigorous low-level circulation this afternoon. Given the lack of scatterometer data today, the initial intensity is kept at 35 kt based on the blend of Dvorak estimates. It will be very difficult for Fred to survive the very strong westerly wind shear which is forecast to continue affecting the cyclone for the next couple of days and the NHC forecast calls for Fred to become a remnant low in about 24 hours. By the end of the forecast period, if Fred has not completely dissipated, the shear could be lighter. This combined with the presence of anomalously warm waters in the North Atlantic, could provide a very small opportunity for Fred to redevelop. The 1200 UTC global models, however, show a less favorable environment for Fred to redevelop than in earlier runs, and perhaps the regeneration will not materialize. A weak to moderate ridge of high pressure over the North Atlantic continues to steer Fred toward the west-northwest or 295 degrees at 10 kt. In a couple of days, Fred or its remnants will be located on the southwestern edge of the ridge, and will begin to move toward the northwest and north. After 3 days, the system will recurve toward the northeast in the mid-latitude westerlies. The NHC forecast continues to be very close to the consensus of the GFS and the ECMWF global models. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 22.0N 35.4W 35 KT 40 MPH 12H 04/0600Z 22.4N 36.8W 35 KT 40 MPH 24H 04/1800Z 22.7N 38.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 05/0600Z 23.0N 40.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/1800Z 23.5N 42.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/1800Z 26.0N 43.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/1800Z 29.0N 40.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/1800Z 31.0N 38.0W 30 KT 35 MPH...TROPICAL DEPRESSION $$ Forecaster Avila

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Tropical Storm FRED Forecast Discussion Number 19

2015-09-03 16:34:21| National Hurricane Center (Atlantic)

Issued at 1100 AM AST THU SEP 03 2015 000 WTNT41 KNHC 031434 TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 1100 AM AST THU SEP 03 2015 As anticipated, a surge of strong upper-level westerly winds removed most of the convection from Fred overnight, and again the cyclone consists of a very vigorous swirl of low clouds. Just like yesterday, a few new convective cells are redeveloping to the north of the center. Assuming that the winds are gradually decaying, the initial intensity has been lowered to 35 kt. The strong upper-level winds affecting Fred are forecast to continue creating a very hostile environment for the cyclone. Consequently, the NHC forecast calls for Fred to become a remnant low in about 12 to 24 hours. By the end of the forecast period, if Fred has not dissipated, models are showing less shear. This combined with the presence of anomalous warm waters in the North Atlantic, will provide a small opportunity for Fred to redevelop some as indicated in the NHC forecast. A weak to moderate ridge of high pressure over the North Atlantic is steering Fred toward the west-northwest or 295 degrees at 9 kt. In a couple of days, Fred or its remnants will be located on the southwestern edge of the ridge, and will begin to move toward the northwest and north. After 3 days, the system will then recurve toward the northeast around the ridge. Although most of the track models provided this solution, the NHC forecast is very close to the consensus of the GFS and the ECMWF global models. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 21.5N 34.1W 35 KT 40 MPH 12H 04/0000Z 21.9N 35.3W 30 KT 35 MPH 24H 04/1200Z 22.3N 37.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 05/0000Z 22.6N 38.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/1200Z 23.0N 40.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/1200Z 25.0N 42.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/1200Z 27.5N 41.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/1200Z 30.5N 38.5W 30 KT 35 MPH...TROPICAL DEPRESSION $$ Forecaster Avila

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Tropical Storm KEVIN Forecast Discussion Number 11

2015-09-03 10:46:50| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU SEP 03 2015 000 WTPZ44 KNHC 030846 TCDEP4 TROPICAL STORM KEVIN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142015 200 AM PDT THU SEP 03 2015 Recent ASCAT data indicate that the cyclone is producing a sizable area of 35-kt winds, especially beneath a burst of deep convection which has persisted during the past few hours. The scatterometer data also indicated that the low-level center is now embedded beneath the southeastern edge of the convective canopy, and Dvorak estimates are a consensus T2.5/35 kt from TAFB and SAB. Based on these data, the cyclone is being upgraded to Tropical Storm Kevin. Although some southerly shear is expected to continue affecting Kevin during the next several days, warm sea surface temperatures and a moist environment could support just a little more strengthening during the next 24 hours. The NHC intensity forecast has been adjusted slightly upward during that period and shows a peak intensity close to the ICON intensity consensus and the Florida State Superensemble. After 36 hours, the shear is likely to allow drier air to get into the circulation, leading to weakening. Kevin is forecast to degenerate to a remnant low by day 3 and dissipate around day 5. With the help of the ASCAT data, the low-level center was adjusted a tad west of where it was previously estimated, and the initial motion estimate is 350/5 kt. Kevin should continue northward between a mid-level anticyclone over Mexico and a deep-layer trough off the west coast of North America for the next 36 hours. Once the cyclone weakens and is no longer producing significant deep convection, the center is expected to turn westward in the low-level flow. The global models appear to be in better agreement on when this turn will occur, and the bulk of the guidance now shows a sharper westward turn after 48 hours. The new NHC track forecast is therefore a bit west of the previous forecast and is close to the TVCE dynamical consensus. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 17.5N 115.3W 35 KT 40 MPH 12H 03/1800Z 18.4N 115.5W 40 KT 45 MPH 24H 04/0600Z 19.6N 115.5W 40 KT 45 MPH 36H 04/1800Z 20.6N 115.4W 35 KT 40 MPH 48H 05/0600Z 21.3N 115.6W 30 KT 35 MPH 72H 06/0600Z 22.1N 117.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/0600Z 22.1N 119.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/0600Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm FRED Forecast Discussion Number 18

2015-09-03 10:46:50| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 03 2015 000 WTNT41 KNHC 030846 TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 500 AM AST THU SEP 03 2015 Fred has made a slight resurgence since the previous advisory with the development of a large cluster of deep convection in the northeastern quadrant, including a narrow band of cloud tops colder than -80C having persisted very near the partly exposed low-level center. The initial intensity has been increased to 40 kt based on a blend of satellite intensity estimates T3.0/45 kt from TAFB, T2.0/30 kt from SAB, and T2.5/35 kt from UW-CIMSS ADT. The initial motion estimate has slowed slightly to 295/07 kt. Otherwise, there remains no change to the forecast track or reasonings mentioned in previous advisory discussions. A shortwave trough currently moving off of the U.S. Mid-Atlantic coast is forecast by the global and regional models to dig east-southeastward into the central Atlantic during the next 5 days, and gradually erode the western portion of the Bermuda-Azores ridge. This will allow Fred to slowly turn northwestward in 48-72 hours, and turn northward at 96 and 120 hours. The NHC guidance is in much better agreement on this developing scenario compared to 24 hours ago. The new official forecast track is essentially just an extension of the previous advisory track and lies close to the consensus models. The GFS and ECMWF models are indicating that more than 30 kt of westerly deep-layer vertical wind shear is affecting Fred. However, this has not kept deep convection from redeveloping near the center, at least for the time being. These strong shear conditions are forecast to persist and even increase during the next 48 hours and, when combined with increasingly drier mid-level air, should induce gradual weakening within the next 12 hours or so. Fred is forecast to weaken to a depression by late tonight or Friday morning, and degenerate into a remnant low by Friday night. By 72 hours and beyond, the remnant low is forecast to reach a more favorable environment of warmer sea surface temperatures, decreasing shear, and increasing moisture, which suggest that there is at least a low probability that regeneration could occur. As a result, the official intensity forecast continues to show a remnant low through 120 h. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 20.8N 33.2W 40 KT 45 MPH 12H 03/1800Z 21.4N 34.5W 35 KT 40 MPH 24H 04/0600Z 21.9N 36.1W 30 KT 35 MPH 36H 04/1800Z 22.2N 37.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 05/0600Z 22.6N 39.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 06/0600Z 24.0N 41.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/0600Z 26.5N 41.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/0600Z 28.8N 40.3W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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