ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Greg Discussion Number 13 NWS National Hurricane Center Miami FL EP072017 800 AM PDT Thu Jul 20 2017 Greg has become notably better organized during the past several hours with a growing curved band stretching around the eastern and southern semicircles of the storm. This organization trend is also seen on a 1139Z SSMIS microwave pass, which shows a better-defined central core. Satellite intensity estimates are between 45-55 kt, and the initial wind speed is set to 45 kt, on the low side since the satellite signature has been above the ASCAT data for the past day or so. The northwesterly shear from yesterday has diminished, leading to a symmetric outflow pattern near the storm. While the SSTs are expected to be warm enough for strengthening for the next few days, the possible interaction of Greg and a mid/upper-level trough near 130W is a complicating factor in the forecast, along with the interaction of the remnants of Eight-E. While both of these features could temporarily cause less favorable conditions, they are not expected to be enough to prevent at least gradual strengthening of Greg. Most of the model guidance is a bit higher than the previous advisory, and the NHC forecast is bumped up from the previous package. This forecast could turn out to be conservative if the favorable environments seen in the HWRF and HMON models materialize. The initial motion estimate is 275/9. A westward to west- northwestward motion is forecast for the next several days while Greg is steered by a ridge to the north. There is some possibility that the aforementioned trough could weaken the ridge enough to induce a more northwestward turn by the end of the forecast, although that is dependent on exactly how far north Greg is at that time. Since the forecast is for a slightly stronger cyclone, which would be more likely to feel the weakness, it makes some sense to shift the track a little northward by day 5. Thus the NHC track forecast is adjusted poleward at long range, but remains south of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 14.1N 115.4W 45 KT 50 MPH 12H 21/0000Z 14.3N 116.7W 50 KT 60 MPH 24H 21/1200Z 14.7N 118.7W 55 KT 65 MPH 36H 22/0000Z 15.1N 120.8W 60 KT 70 MPH 48H 22/1200Z 15.4N 122.9W 65 KT 75 MPH 72H 23/1200Z 16.0N 127.5W 65 KT 75 MPH 96H 24/1200Z 16.3N 131.5W 55 KT 65 MPH 120H 25/1200Z 17.0N 135.0W 45 KT 50 MPH $$ Forecaster Blake NNNN
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