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Tropical Depression TWELVE-E Forecast Discussion Number 2

2016-08-19 04:47:25| Tropical Depression LIDIA

Issued at 900 PM MDT THU AUG 18 2016

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Tropical Storm FIONA Forecast Discussion Number 9

2016-08-19 04:43:23| National Hurricane Center (Atlantic)

Issued at 1100 PM AST THU AUG 18 2016 000 WTNT41 KNHC 190243 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST THU AUG 18 2016 A sizable burst of deep convection has been ongoing since late this afternoon, and recent microwave imagery suggests that the low-level center may be a little closer to the thunderstorm activity than it was for most of the day. Still, Dvorak estimates are unchanged at T3.0/45 kt from TAFB and T2.5/35 kt from SAB, and the initial intensity remains 40 kt. Fiona's window for any strengthening is narrowing. SHIPS guidance is currently analyzing 10-15 kt of south-southwesterly shear, while the UW-CIMSS analysis has the shear as high as 20-25 kt. Despite the discrepancy, these values suggest the shear is already increasing, and it is expected to increase further and become more westerly during the next three days. Therefore, if the current burst of convection continues, Fiona has a chance to strengthen slightly during the next 12 hours and then gradually weaken through days 3 and 4. The forecast trends in the intensity models suggest that Fiona could weaken to a tropical depression, which is now shown in the official forecast. Environmental conditions appear to be a little less hostile by the end of the forecast period, and the NHC forecast allows for the possibility that Fiona could restrengthen after the shear lightens up. The GFDL continues to be an outlier by intensifying Fiona more than the other models, and the official intensity forecast is therefore near or just below the intensity consensus for most of the forecast period. Microwave fixes indicate that Fiona has been moving more slowly toward the northwest, or 305/7 kt. The cyclone is moving toward a break in the subtropical ridge located between 40W-55W, and an amplifying deep-layer trough over the north Atlantic is expected to maintain this break for the next several days. By continuing on a northwestward heading, Fiona is expected to reach the axis of the subtropical ridge and turn northward by day 5. The GFDL is still well to the northeast of the rest of the track guidance since it carries a much stronger system, but the other models are otherwise in very good agreement. Therefore, no significant changes were made to the NHC track forecast, which remains close to the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 17.1N 41.8W 40 KT 45 MPH 12H 19/1200Z 17.8N 43.1W 45 KT 50 MPH 24H 20/0000Z 18.7N 44.9W 40 KT 45 MPH 36H 20/1200Z 19.8N 46.9W 35 KT 40 MPH 48H 21/0000Z 20.9N 48.9W 35 KT 40 MPH 72H 22/0000Z 23.0N 53.2W 30 KT 35 MPH 96H 23/0000Z 25.0N 56.5W 30 KT 35 MPH 120H 24/0000Z 27.5N 57.0W 35 KT 40 MPH $$ Forecaster Berg

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Tropical Storm FIONA Forecast Discussion Number 8

2016-08-18 22:37:47| National Hurricane Center (Atlantic)

Issued at 500 PM AST THU AUG 18 2016 000 WTNT41 KNHC 182037 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 PM AST THU AUG 18 2016 After a brief convective hiatus, deep convection with cloud tops of -70C to -75C has redeveloped into a small CDO feature directly over the previously exposed low-level circulation center. Satellite classifications are T3.0/45 kt and T2.5/35 kt from TAFB and SAB, respectively, and UW-CIMSS ADT values have decreased to T3.0/45 kt. A blend of these values support an initial intensity of 40 kt. Fiona is moving a little faster toward the northwest, or 300/09 kt. Other than minor fluctuations in the forward speed of the cyclone due to intermittent periods of convective re-organization like the most recent episode, the latest model guidance continues to be in strong agreement on Fiona moving west-northwestward to northwestward toward a break in the Bermuda-Azores High for the next 120 hours. Given the tightly packed model guidance about the previous few forecast tracks, the new NHC track forecast is just an extension of the previous advisory, and lies close to but a little slower than the consensus model, TVCN. There is no significant change to the previous intensity forecast or rationale. Despite the earlier sharp decrease in deep convection, the inner-core wind field of the compact cyclone has remained quite robust based on the lack of no arc cloud lines or outflow boundaries seen emanating outward from the center in visible satellite today. As result, Fiona should be able to generate additional convection in the short term and strengthen some during the next 12-24 hours. After that time, the global and regional models remain in good agreement on the cyclone moving through a band of strong southwesterly vertical wind shear of 20-25 kt from 36-72 hours, which is expected to induce weakening. However, the amount of weakening remains uncertain due to continued mixed dynamic and thermodynamic conditions. Although Fiona will be propagating through significant shear and into a drier airmass, the small cyclone will also be moving over warmer SSTs of 28C-29C and into a region of much cooler upper-tropospheric temperatures, which will produce greater instability and generate fairly strong convection that could help offset the unfavorable shear conditions. Given these mixed signals, the official intensity forecast remains an average of the various intensity models, which at 72 hours still ranges from hurricane strength in the GFDL model to a 25-kt remnant low in the ECMWF and Navy-CTCI models. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 17.0N 41.3W 40 KT 45 MPH 12H 19/0600Z 17.7N 42.5W 45 KT 50 MPH 24H 19/1800Z 18.5N 44.3W 45 KT 50 MPH 36H 20/0600Z 19.6N 46.1W 35 KT 40 MPH 48H 20/1800Z 20.8N 48.0W 35 KT 40 MPH 72H 21/1800Z 23.0N 51.7W 35 KT 40 MPH 96H 22/1800Z 25.0N 55.0W 35 KT 40 MPH 120H 23/1800Z 27.2N 56.6W 35 KT 40 MPH $$ Forecaster Stewart

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Tropical Storm FIONA Forecast Discussion Number 6

2016-08-18 14:41:47| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU AUG 18 2016 000 WTNT41 KNHC 181241 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 6...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST THU AUG 18 2016 Corrected track guidance discussion in third paragraph Deep convection associated with Fiona has increased with the approach of the diurnal convective maximum, and the cyclone's cloud pattern is better organized than it was yesterday. Satellite data suggest that the low-level center is now located underneath an irregularly shaped central dense overcast, while a few broken banding features have recently developed over the eastern semicircle of the circulation. Satellite classifications are T3.0/45 kt and T2.0/30 kt from TAFB and SAB, respectively, while ADT values are around T3.0. A blend of these data is used to increase the initial wind speed to 40 kt. Global models indicate that large-scale conditions should be adequately conducive to support some additional strengthening during the next 12 to 24 hours. However, after that time, a substantially drier atmosphere and increasing southwesterly shear associated with the mid-oceanic trough are expected to induce weakening, even though sea surface temperatures will be higher. Although not shown explicitly in the forecast, atmospheric conditions could become so hostile that Fiona would degenerate into a remnant low later in the forecast period as depicted in the ECMWF model. The new NHC intensity forecast is slightly higher than the previous one and the bulk of the guidance in the short term but is a little lower after 48 hours. Fiona has been moving west-northwestward to northwestward into a weakness in the mid-level subtropical ridge between 40w and 50w, and the initial motion estimate is 300/14. Fiona should maintain a similar heading but at a reduced forward speed once it becomes a shallower cyclone in a few days and is steered around the Atlantic low-level subtropical ridge. The NHC track forecast has been adjusted to the north of the previous one, mostly after 48 hours and largely in response to a significant shift in the latest ECMWF solution. The forecast track lies on the western side of the guidance envelope, well to the left of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 16.2N 40.3W 40 KT 45 MPH 12H 18/1800Z 17.0N 41.4W 45 KT 50 MPH 24H 19/0600Z 17.9N 43.0W 50 KT 60 MPH 36H 19/1800Z 18.7N 44.6W 45 KT 50 MPH 48H 20/0600Z 19.8N 46.6W 40 KT 45 MPH 72H 21/0600Z 22.1N 50.1W 35 KT 40 MPH 96H 22/0600Z 23.8N 53.5W 35 KT 40 MPH 120H 23/0600Z 25.6N 56.1W 35 KT 40 MPH $$ Forecaster Kimberlain

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Tropical Storm FIONA Forecast Discussion Number 6

2016-08-18 10:40:16| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU AUG 18 2016 000 WTNT41 KNHC 180840 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST THU AUG 18 2016 Deep convection associated with Fiona has increased with the approach of the diurnal convective maximum, and the cyclone's cloud pattern is better organized than it was yesterday. Satellite data suggest that the low-level center is now located underneath an irregularly shaped central dense overcast, while a few broken banding features have recently developed over the eastern semicircle of the circulation. Satellite classifications are T3.0/45 kt and T2.0/30 kt from TAFB and SAB, respectively, while ADT values are around T3.0. A blend of these data is used to increase the initial wind speed to 40 kt. Global models indicate that large-scale conditions should be adequately conducive to support some additional strengthening during the next 12 to 24 hours. However, after that time, a substantially drier atmosphere and increasing southwesterly shear associated with the mid-oceanic trough are expected to induce weakening, even though sea surface temperatures will be higher. Although not shown explicitly in the forecast, atmospheric conditions could become so hostile that Fiona would degenerate into a remnant low later in the forecast period as depicted in the ECMWF model. The new NHC intensity forecast is slightly higher than the previous one and the bulk of the guidance in the short term but is a little lower after 48 hours. Fiona has been moving west-northwestward to northwestward into a weakness in the mid-level subtropical ridge between 40w and 50w, and the initial motion estimate is 300/14. Fiona should maintain a similar heading but at a reduced forward speed once it becomes a shallower cyclone in a few days and is steered around the Atlantic low-level subtropical ridge. The NHC track forecast has been adjusted to the north of the previous one, mostly after 48 hours and largely in response to a significant shift in the latest ECMWF solution. The forecast track lies on the far eastern side of the guidance envelope, well to the left of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 16.2N 40.3W 40 KT 45 MPH 12H 18/1800Z 17.0N 41.4W 45 KT 50 MPH 24H 19/0600Z 17.9N 43.0W 50 KT 60 MPH 36H 19/1800Z 18.7N 44.6W 45 KT 50 MPH 48H 20/0600Z 19.8N 46.6W 40 KT 45 MPH 72H 21/0600Z 22.1N 50.1W 35 KT 40 MPH 96H 22/0600Z 23.8N 53.5W 35 KT 40 MPH 120H 23/0600Z 25.6N 56.1W 35 KT 40 MPH $$ Forecaster Kimberlain

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