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Tropical Depression SEVEN Forecast Discussion Number 1

2016-08-22 22:35:21| National Hurricane Center (Atlantic)

Issued at 500 PM AST MON AUG 22 2016 000 WTNT42 KNHC 222035 TCDAT2 TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 PM AST MON AUG 22 2016 The low pressure area located west-southwest of the Cabo Verde Islands has developed a well-defined circulation and sufficient organized convection to be considered a tropical depression. Microwave imagery suggests that the system is likely still consolidating, with two or more vorticity centers rotating around a mean center. The initial intensity is set to 30 kt in agreement with a satellite intensity estimate from TAFB. The initial motion is 275/16. The cyclone is on the south side of a deep-layer ridge over the eastern Atlantic, and as a result it should move generally west-northwestward for the next 36-48 hours. Beyond that time, the cyclone is forecast to turn northwestward toward a weakness in the ridge over the central Atlantic. The track guidance is in good agreement with this scenario, and the forecast track lies near the consensus models. The depression is currently in an environment of light to moderate easterly vertical shear. This, combined with warm sea surface temperatures, should allow strengthening. One possible negative factor, however, is a tongue of African dust/dry air wrapping around the west side of the circulation. On that basis that the dry air will not stop development, the intensity forecast calls for steady strengthening through 72 hours. After that time, arrested development is likely due to the cyclone encountering moderate to strong westerly vertical shear. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 12.1N 29.0W 30 KT 35 MPH 12H 23/0600Z 12.4N 31.4W 40 KT 45 MPH 24H 23/1800Z 13.2N 34.4W 50 KT 60 MPH 36H 24/0600Z 14.5N 37.2W 60 KT 70 MPH 48H 24/1800Z 16.2N 39.9W 70 KT 80 MPH 72H 25/1800Z 19.7N 44.8W 80 KT 90 MPH 96H 26/1800Z 23.8N 50.1W 75 KT 85 MPH 120H 27/1800Z 26.8N 54.0W 75 KT 85 MPH $$ Forecaster Beven/Roberts

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Tropical Depression FIONA Forecast Discussion Number 23

2016-08-22 16:34:16| National Hurricane Center (Atlantic)

Issued at 1100 AM AST MON AUG 22 2016 000 WTNT41 KNHC 221434 TCDAT1 TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 AM AST MON AUG 22 2016 The satellite depiction of Fiona currently features an exposed low-level circulation with a few small areas of convection southeast of the center. Subjective satellite intensity estimates from TAFB and SAB are 30 kt, while the various objective estimates range from 25-45 kt. The initial intensity remains 30 kt based mainly on the subjective estimates. The dynamical models forecast that the current westerly vertical shear will subside somewhat by 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. Based on the premise that the cyclone will not be able to respond to the brief period of more favorable conditions, the new intensity forecast calls for Fiona to gradually decay and become a remnant low in about 36 hours. This would be followed by the system weakening to a trough after 96 hours. The initial motion is 285/16. The guidance remains in good agreement on the forecast track through 72 hours, with Fiona moving west-northwestward to northwestward toward a developing break 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 will compromise between these extremes in showing a slow north-northwestward motion. The new forecast track is shifted a little to the west of the previous track and lies near the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 24.6N 59.7W 30 KT 35 MPH 12H 23/0000Z 25.3N 61.5W 30 KT 35 MPH 24H 23/1200Z 26.1N 63.5W 30 KT 35 MPH 36H 24/0000Z 27.0N 65.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 24/1200Z 28.1N 66.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/1200Z 30.0N 68.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/1200Z 31.5N 68.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/1200Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression FIONA Forecast Discussion Number 22

2016-08-22 10:42:45| National Hurricane Center (Atlantic)

Issued at 500 AM AST MON AUG 22 2016 000 WTNT41 KNHC 220842 TCDAT1 TROPICAL DEPRESSION FIONA DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST MON AUG 22 2016 Although deep convection has continued to pulse near the center of Fiona, recent scatterometer wind data and various satellite classifications support maintaining the small but remarkably resilient cyclone as a 30-kt tropical depression. The intensity forecast still remains something of an enigma. Strong westerly wind shear is forecast to persist for the next 12-18 hours, after which the upper-level winds relax somewhat and become a little more conducive for strengthening to occur. However, dry mid-level air of 40-50 percent humidity is also forecast to surround the cyclone, which could act to hinder the development of persistent deep convection for the next 24-36 hours. Therefore, if Fiona can survive the aforementioned hostile conditions during the next 24 hours or so, then some restrengthening or maintaining the status as a tropical cyclone is possible. The global models still disagree on the future of Fiona and have flipped-flopped, with the ECMWF no longer showing dissipation in 5 days, which is similar to the UKMET solution, whereas the GFS now shows Fiona degenerating into an open trough between 96-120 hours. The NHC forecast maintains continuity and indicates dissipation in 5 days as a compromise between these possibilities. The initial motion estimate remains 290/16 kt. Although there is uncertainty in the future status of Fiona, the NHC model guidance is in pretty good agreement on the track of the cyclone for the next 72 hours. The small cyclone is forecast to move quickly west-northwestward around the southwestern periphery of a deep-layer ridge for the next 3 days, and then slow down considerably on day 4 and turn northward into a weakness in the ridge. The new official forecast track is basically just an update of the previous track through 72 hours, and then is a little to the right of the previous forecast on day 4, which leans closer to the solutions of the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 24.4N 58.4W 30 KT 35 MPH 12H 22/1800Z 25.0N 60.2W 30 KT 35 MPH 24H 23/0600Z 25.8N 62.3W 30 KT 35 MPH 36H 23/1800Z 26.6N 64.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 24/0600Z 27.6N 65.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 25/0600Z 29.8N 67.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 26/0600Z 31.3N 67.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 27/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm KAY Forecast Discussion Number 12

2016-08-21 16:42:12| Tropical Depression LIDIA

Issued at 900 AM MDT SUN AUG 21 2016

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Tropical Storm FIONA Forecast Discussion Number 18

2016-08-21 10:51:14| National Hurricane Center (Atlantic)

Issued at 500 AM AST SUN AUG 21 2016 000 WTNT41 KNHC 210851 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST SUN AUG 21 2016 After the earlier convective bursting episode and resultant spin up of the low-level wind field, strong westerly shear of at least 30 kt has stripped away the convective cloud shield, leaving a fully exposed low-level circulation center that is easy to locate. Assuming some spin down of the circulation due to the loss of convection, the initial intensity has been lowered to 40 kt. Now that Fiona's circulation has become a little more shallow, the low-level center has turned more westward and the cyclone is now moving 295/14 kt. The global models are in good agreement on a mid-level ridge to the north and northeast of Fiona remaining in place for the next few days, which should keep the small cyclone moving in a general west-northwest direction through 72 hours. After that time, the western portion of the ridge is expected to weaken due to an approaching frontal system, which should allow Fiona or its remnant circulation to slow down and turn northwestward. The new track forecast is essentially just an update of the previous advisory track, and lies close to the TVCN consensus model forecast. During the next 24 hours or so, Fiona is forecast to traverse through a band of strong westerly to northwesterly vertical wind shear of 25-30 kt and dry mid-level air with humidity values near 40 percent. As a result, gradual weakening is expected due to the small cyclone likely not being able to sustain deep convection for long periods of time. The new intensity forecast holds onto the previous trend of Fiona weakening into a remnant low by 72 hours. However, a lot of uncertainty remains with this intensity forecast. Strong instability that will be present due to very warm SSTs of 29C-30C and a cool upper-level troposphere, which could produce periodic bursts of intense convection that could sustain the low-level vortex until environmental become more favorable for strengthening on days 4 and 5. Most of the global models continue to depict a weak low for at least the next 5 days, except for the ECMWF model, which weakens Fiona to an open trough by 48 hours. The NHC intensity remains a compromise of these extremes and shows dissipation by day 5. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 22.2N 51.7W 40 KT 45 MPH 12H 21/1800Z 22.9N 53.7W 35 KT 40 MPH 24H 22/0600Z 23.8N 56.3W 35 KT 40 MPH 36H 22/1800Z 24.5N 58.6W 35 KT 40 MPH 48H 23/0600Z 25.3N 60.7W 30 KT 35 MPH 72H 24/0600Z 27.0N 64.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 25/0600Z 29.7N 66.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 26/0600Z...DISSIPATED $$ Forecaster Stewart

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