000 WTPZ42 KNHC 152037 TCDEP2 Tropical Storm Tara Discussion Number 6 NWS National Hurricane Center Miami FL EP222018 400 PM CDT Mon Oct 15 2018 Tara is now a tiny tropical storm consisting of a small, circular area of intense convection that continues to go through bursting phases. Two recent ASCAT scatterometer passes revealed that the persistent cold overshooting cloud tops of -85C to -90C near the center has apparently stretched the vortex column vertically, causing the intensity to increase and wind field to shrink. The 34-kt wind radii have contracted down to about 20 nmi, and the outermost circulation has decreased to only about 140 nmi wide. The highest ASCAT wind speed value measured was 40 kt on both passes. However, actual peak winds were likely undersampled given that they were observed at a distance of only 10 nmi from the center. The initial intensity has been increased to 45 kt based on a Dvorak satellite intensity estimate of T3.0/45 kt from both TAFB and SAB, an objective UW-CIMSS ADT estimate of T3.4/53 kt and a SATCON estimate of 48 kt, and this estimate is probably conservative. The initial motion estimate is an uncertain 305/02 kt. Tara's center has likely re-developed closer to the strong convective bursts that had been occuring just north of the previous low-level center. As such, the exact direction and speed of the tiny tropical cyclone is difficult to ascertain. Recent scatterometer and visible satellite data suggest that Tara may have become stationary or is making a tight loop. All of the global and regional models now keep the tiny tropical cyclone offshore for the entire 120-h forecast period, and the new NHC model guidance indicates that a slow, erratic motion toward the west-northwest or northwest should occur for the next five days while Tara remains embedded within a weak steering flow regime. The new official track forecast follows the trend of the previous few advisory tracks, and lies near a blend of the HCCA, FSSE, and TVCE consensus models. However, due to the continued large spread in the guidance, the track forecast is of low to moderate confidence. The intensity forecast is problematic due to Tara's very small circulation since tiny tropical cyclones can both spin up or spin down very quickly. Moderate easterly to southeasterly vertical wind shear is forecast to continue for the next 24 hours or so, followed by a pronounced decrease in the shear until 48-72 hours. These conditions should allow for a slow but steady increase in the intensity. However, during the 36-to-60-hour period when the shear will be the lowest, more significant strengthening could occur due to Tara's small circulation. However, none of the guidance brings the tiny cyclone to hurricane strength. By days 4 and 5, southwesterly wind shear is forecast to increase to around 20 kt, which is expected to induce gradual weakening. Due to Tara's small circulation, the official intensity forecast is slightly higher than the consensus models HCCA, IVCN, and FSSE, and closely follows the LGEM statistical-dynamical intensity forecast aid. Regardless of how close Tara comes to southwestern Mexico, heavy rainfall will continue to 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 15/2100Z 18.0N 104.5W 45 KT 50 MPH 12H 16/0600Z 18.1N 104.7W 50 KT 60 MPH 24H 16/1800Z 18.2N 104.9W 55 KT 65 MPH 36H 17/0600Z 18.2N 105.4W 55 KT 65 MPH 48H 17/1800Z 18.2N 106.0W 55 KT 65 MPH 72H 18/1800Z 18.7N 107.3W 55 KT 65 MPH 96H 19/1800Z 18.8N 108.2W 50 KT 60 MPH 120H 20/1800Z 18.5N 108.4W 45 KT 50 MPH $$ Forecaster Stewart