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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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