000 WTPZ42 KNHC 150852 TCDEP2 Tropical Storm Tara Discussion Number 4 NWS National Hurricane Center Miami FL EP222018 400 AM CDT Mon Oct 15 2018 The satellite presentation of the tropical cyclone has improved somewhat overnight, with convection continuing to burst over the western and northwestern portions of the circulation. The center is slightly more embedded within the southeastern portion of the cold cloud tops, but easterly shear continues to restrict convection over the eastern portion of the system. A couple of ASCAT passes around 0400 UTC were helpful in locating the center of the cyclone and both indicated peak winds of 25 to 30 kt to the west of the center. Dvorak classifications at 0600 UTC were T2.5 (35 kt) from both SAB and TAFB, and given the increase in organization, the system has been upgraded to a 35-kt tropical storm. The nineteenth named storm of the 2018 eastern North Pacific hurricane season. Recent microwave imagery and the ASCAT data show that Tara has not moved much, and the initial motion estimate is stationary for this advisory. Although the tropical storm is located within an area of weak steering currents and little overall motion is expected during the next couple of days, the track guidance has become much more divergent this cycle. The GFS and UKMET models have trended northward and now bring Tara near the southwestern coast of Mexico within the next day or so. On the other hand, the ECMWF takes Tara southeastward and southward away from the coast. The various consensus aids have trended northward in the short-term, and the new NHC track forecast has been nudged in that direction through 36 hours, but it is not as far north as the GFS, GFS ensemble mean, and UKMET models. After 48 hours, a ridge is forecast to build westward across central Mexico, which should cause Tara to turn west-northwestward at a slightly faster forward speed. Given the spread in the guidance and its recent trends, the track forecast is of low confidence. The intensity forecast is also very challenging and of low confidence this morning. Tara is expected to remain under the influence of easterly shear during the next day or two. The shear, however, is not expected to be strong enough to prevent gradual strengthening. After that time, the intensity forecast depends on how close to the coast the cyclone moves. If Tara gets too close to southwestern Mexico, the small cyclone is likely to weaken. If it stays offshore, however, the shear is forecast to decrease which should allow for additional strengthening. Since the NHC track forecast keeps Tara offshore, it calls for gradual strengthening through 72 hours, but it is not as aggressive as before since most of the guidance is lower than before. Increasing southwesterly shear by days 4 and 5 should lead to weakening, and although the NHC forecast keeps Tara a tropical storm trough the period, most of the global models weaken and dissipate the system by the end of the week. Due to the uncertainties in the track forecast, the government of Mexico has issued a Tropical Storm Watch for a portion of the coast of southwest Mexico. Regardless of how close Tara tracks to southwestern Mexico, heavy rainfall will be the primary threat along the coast of southwestern Mexico due to the system's slow motion, and life-threatening flash flooding will be possible in mountainous areas. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 17.5N 104.2W 35 KT 40 MPH 12H 15/1800Z 17.8N 104.4W 40 KT 45 MPH 24H 16/0600Z 17.9N 104.5W 45 KT 50 MPH 36H 16/1800Z 17.9N 104.7W 45 KT 50 MPH 48H 17/0600Z 18.0N 105.3W 50 KT 60 MPH 72H 18/0600Z 18.3N 106.5W 55 KT 65 MPH 96H 19/0600Z 19.0N 108.0W 50 KT 60 MPH 120H 20/0600Z 19.0N 108.0W 45 KT 50 MPH $$ Forecaster Brown