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 143 
 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
 
 
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