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Tropical Storm GASTON Forecast Discussion Number 3

2016-08-23 10:41:32| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE AUG 23 2016 000 WTNT42 KNHC 230841 TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 AM AST TUE AUG 23 2016 Thunderstorm activity has continued to become better organized since the previous advisory, especially in the inner-core region. In addition, a 0556Z GPM microwave overpass indicated that a 15-20-nmi-diameter, closed low-level eye feature had developed. The initial intensity as been increased to 45 kt based on a consensus Dvorak satellite intensity estimate of T3.0/45 kt from TAFB and SAB, which is supported by a UW-CIMSS ADT value of T2.9/43 kt. The initial motion estimate is 290/17 kt. Gaston is expected to move west-northwestward for the next 72 hours along the southern periphery of a deep-layer ridge located to the north and northeast of the cyclone. After that time, a gradual turn toward the northwest is forecast as Gaston moves into a break in the subtropical ridge. The models are in excellent agreement on this track scenario and are closely packed through day 3, with a large spread in the model tracks occurring after that time due to differences in the timing of when Gaston will make the poleward turn through the break in the ridge. The official forecast is similar to the previous advisory track, and lies a little to the left of the consensus model TVCN. The aforementioned eye feature, in conjunction with low shear conditions, well-defined upper-level anticyclonic outflow, SSTs near 28 deg C, and mid-level humidity values near 70 percent, generally would support a period of rapid intensification for the next 24 hours or so. However, the current forecast follows the trend of the previous advisory and shows strengthening at a more typical rate of 20 kt/24h for the next 36 hours due to a narrow band of dry air that appears to have penetrated into the inner core, which will take some time to mix out. After that time, the intensity is leveled off due to the cyclone moving through a band of strong southwesterly vertical wind shear, which should disrupt both the convective and upper-level outflow patterns. The initial intensity is near the IVCN intensity consensus model through 24 hours, and then a little above that and near the SHIPS model. However, the new intensity forecast lies well below the GFS model output, which is forecasting Gaston to become a major hurricane around 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 13.2N 32.4W 45 KT 50 MPH 12H 23/1800Z 13.9N 34.8W 55 KT 65 MPH 24H 24/0600Z 15.2N 37.9W 65 KT 75 MPH 36H 24/1800Z 16.8N 40.6W 75 KT 85 MPH 48H 25/0600Z 18.5N 43.0W 80 KT 90 MPH 72H 26/0600Z 22.6N 47.4W 80 KT 90 MPH 96H 27/0600Z 26.5N 51.5W 80 KT 90 MPH 120H 28/0600Z 29.4N 53.6W 80 KT 90 MPH $$ Forecaster Stewart

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Tropical Storm KAY Forecast Discussion Number 18

2016-08-23 04:35:19| Tropical Depression LIDIA

Issued at 800 PM PDT MON AUG 22 2016

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Tropical Depression FIONA Forecast Discussion Number 25

2016-08-23 04:34:21| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON AUG 22 2016 000 WTNT41 KNHC 230234 TCDAT1 TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST MON AUG 22 2016 Fiona is a very disorganized tropical cyclone. The associated deep convection has been sputtering and lacking in organization. The current intensity is held at 30 kt in accordance with a Dvorak estimate from TAFB. Strong westerly shear has been affecting the tropical cyclone, but this shear is forecast to abate in 12 to 24 hours as the system moves away from an upper-level trough and into a region of upper-level easterlies. By 48 hours or so, however, the shear over the cyclone should be increasing due to another trough just off the U.S. east coast. Given its current state, Fiona is not expected to take much advantage from the reduced shear and instead will likely degenerate into a remnant low in 48 hours, or sooner. The official intensity forecast is below the consensus guidance, and follows the trend shown in the global models. The center is not easy to locate on night time imagery, but the best guess at the initial motion is a slightly slower 290/13 kt. Fiona is expected to turn northwestward with some deceleration as it heads for a break in the subtropical ridge. The official track forecast is very close to the latest dynamical model consensus, TVCN. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 25.5N 62.3W 30 KT 35 MPH 12H 23/1200Z 25.9N 63.8W 30 KT 35 MPH 24H 24/0000Z 26.7N 65.8W 25 KT 30 MPH 36H 24/1200Z 27.7N 67.6W 25 KT 30 MPH 48H 25/0000Z 28.7N 68.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/0000Z 30.0N 70.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 27/0000Z 30.5N 71.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 28/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm GASTON Forecast Discussion Number 2

2016-08-23 04:31:49| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON AUG 22 2016 000 WTNT42 KNHC 230231 TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 PM AST MON AUG 22 2016 The convective organization of the tropical cyclone has continued to increase this evening. A couple of well-defined curved bands of convection now wrap more than halfway around the center and some cold cloud tops have recently developed near the center. As a result, subjective Dvorak T-numbers have increased to T2.5 and support upgrading the system to a 35-kt tropical storm. Gaston becomes the seventh tropical storm of the 2016 Atlantic hurricane season. Gaston is forecast to move over warm water and remain in a low wind shear environment during the next couple of days. These favorable conditions should allow for steady strengthening, and Gaston is forecast to become a hurricane in about 36 hours, which agrees with the majority of the intensity guidance. In about 3 days, the global models suggest that Gaston will be nearing an upper-level low over the central Atlantic that could cause an increase in southwesterly shear over the system. This should halt intensification, and the NHC forecast calls for little change in strength after 72 hours. The tropical storm is being steered west-northwestward to the south of deep-layer ridge over the eastern Atlantic. A west-northwestward motion with some decrease in forward speed is expected during the next day or so. After that time, a weakness in the subtropical ridge over the central Atlantic should cause Gaston to turn northwestward. The track guidance remains in very good agreement, and the NHC forecast is close to the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 12.6N 30.7W 35 KT 40 MPH 12H 23/1200Z 13.0N 33.1W 45 KT 50 MPH 24H 24/0000Z 14.0N 36.0W 55 KT 65 MPH 36H 24/1200Z 15.3N 38.6W 65 KT 75 MPH 48H 25/0000Z 17.1N 41.1W 75 KT 85 MPH 72H 26/0000Z 21.0N 46.0W 80 KT 90 MPH 96H 27/0000Z 25.0N 50.5W 75 KT 85 MPH 120H 28/0000Z 28.0N 53.5W 75 KT 85 MPH $$ Forecaster Brown

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Tropical Depression FIONA Forecast Discussion Number 24

2016-08-22 22:37:19| National Hurricane Center (Atlantic)

Issued at 500 PM AST MON AUG 22 2016 000 WTNT41 KNHC 222037 TCDAT1 TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 PM AST MON AUG 22 2016 A new burst of convection has developed near the center of Fiona during the past several hours. However, this increase was not significant enough to affect the subjective satellite intensity estimates, which remain at 30 kt. This is also in good agreement with earlier ASCAT data. The dynamical models forecast that the current westerly vertical shear will subside somewhat by 36-48 hours as Fiona moves under an upper-level trough into an area of easterly upper-level winds to the north of the trough. By 72 hours, the models forecast the cyclone or its remnants to encounter a second trough, which should produce another round of strong southwesterly shear. The intensity forecast is still based on the premise that the cyclone will not be able to respond to the brief period of more favorable conditions, and it calls for Fiona to gradually decay and become a remnant low in about 48 hours. This should be followed by the system weakening to a trough after 96 hours. The initial motion is 285/15. The guidance remains in good agreement on the forecast track through 72 hours, with Fiona moving west-northwestward to northwestward toward a weakness in the subtropical ridge. Beyond that time, the guidance diverges, with the ECMWF turning the remnants of the system northeastward while the GFS and UKMET show a westward turn. The new forecast track is again a compromise between these extremes in showing a slow north-northwestward motion. Overall, the track guidance has shifted westward since the previous advisory, and as a result the forecast track has also shifted a little to the west. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 25.1N 61.3W 30 KT 35 MPH 12H 23/0600Z 25.6N 63.1W 30 KT 35 MPH 24H 23/1800Z 26.5N 65.0W 30 KT 35 MPH 36H 24/0600Z 27.4N 66.7W 30 KT 35 MPH 48H 24/1800Z 28.3N 67.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/1800Z 30.5N 69.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/1800Z 31.5N 70.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/1800Z...DISSIPATED $$ Forecaster Beven

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