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Tropical Depression Three Forecast Discussion Number 3
2018-07-07 10:53:11| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Sat Jul 07 2018 000 WTNT43 KNHC 070853 TCDAT3 Tropical Depression Three Discussion Number 3 NWS National Hurricane Center Miami FL AL032018 500 AM EDT Sat Jul 07 2018 A pair of late-arriving ASCAT passes at 0136 UTC and 0216 UTC revealed the the depression has not yet strengthened, and its circulation remains very broad. Although the larger-scale circulation of the cyclone is well-defined, it lacks an inner core, and the center of circulation consists of a wide area of light winds. The initial intensity has been held at 25 kt based primarily on the ASCAT data, and this is also supported by the latest Dvorak classifications from TAFB and SAB. While the cyclone was nearly devoid of deep convection for several hours late last night and early this morning, a broken convective band has since developed to the south of the low-level center. This could indicate that the depression is beginning to become better organized and will begin to slowly strengthen. Warm SSTs will likely allow the depression to gradually strengthen through the next 3 to 4 days, however moderate shear and the lack of an existing inner-core will likely limit the intensification rate. The intensity guidance has come into better agreement since yesterday, and now most of the models show the cyclone nearing or reaching hurricane strength. No change has been made to the NHC intensity forecast, which is now near the middle of the guidance and very close to HCCA throughout the forecast. Nighttime Proxy-Vis imagery has been very helpful in tracking the depression this morning, which has slowed down and is now estimated to be moving north-northwestward or 345/4 kt. For the first 48 h, the track models remain in fairly good agreement that the cyclone will meander off the coast of the Carolinas, as it becomes trapped in the light steering flow between a cold front passing to the north and the subtropical ridge to the east. Beyond that time, there has been a significant change in the track models, all of which now depict a much faster northeastward motion beginning on Tuesday as the cyclone recurves ahead of a mid-level trough approaching from the northwest. Although the NHC track forecast has been adjusted to show a faster motion at day 4 and 5, it is now much slower than all of the global models in an effort to maintain continuity from our earlier forecasts. If this trend continues, larger changes will need to be made to the track forecast in future advisories. Most of the guidance continues to suggest that the tropical-storm-force winds associated with the cyclone will occur primarily to the east of the cyclone's center well away from the U.S. coast. Therefore, no watches or warnings are required for the U.S coast at this time, however, interests along the North Carolina coast should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 33.2N 74.6W 25 KT 30 MPH 12H 07/1800Z 33.6N 74.8W 30 KT 35 MPH 24H 08/0600Z 33.8N 74.5W 35 KT 40 MPH 36H 08/1800Z 33.9N 74.0W 40 KT 45 MPH 48H 09/0600Z 34.0N 73.6W 45 KT 50 MPH 72H 10/0600Z 34.5N 72.5W 55 KT 65 MPH 96H 11/0600Z 37.0N 69.0W 65 KT 75 MPH 120H 12/0600Z 41.0N 63.5W 65 KT 75 MPH $$ Forecaster Zelinsky
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