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Tropical Storm RACHEL Forecast Discussion Number 12
2014-09-27 10:38:48| National Hurricane Center (East Pacific)
Issued at 200 AM PDT SAT SEP 27 2014 000 WTPZ43 KNHC 270838 TCDEP3 TROPICAL STORM RACHEL DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 200 AM PDT SAT SEP 27 2014 Rachel's convective structure has evolved since the last advisory. The long curved band noted earlier has become broken and is separated from a small, compact area of deep convection which has developed over the low-level center. An eye-like feature has also occasionally appeared in infrared satellite imagery. Maximum winds are held at 55 kt based on a consensus of T3.5/55 kt Dvorak estimates from TAFB and SAB. Rachel is forecast to be in a low-shear environment for the next 36 hours or so, and the atmosphere should be sufficiently moist and unstable to support some strengthening in the short term. After 48 hours, southwesterly vertical shear of 15-20 kt is forecast to develop, and Rachel will be moving into a much drier and stable environment. The intensity models are in good agreement that Rachel should be at or just below hurricane intensity in 24 hours, which is indicated in the official forecast. Thereafter, the dynamical models show a faster rate of weakening than the statistical models, and the NHC forecast closely follows the multi-model consensus ICON. Rachel has turned northwestward, or 315/7 kt, into a weakness in the subtropical ridge caused by two deep-layer lows over California and the Rio Grande Valley. As the low over California moves eastward, steering currents are expected to collapse, and Rachel should turn north-northwestward but slow down and become nearly stationary in 2-3 days. Once vertical shear increases on day 3, a less-vertically-deep Rachel is expected to begin drifting southwestward in the prevailing low-level flow. The GFS, GFDL, and GFDL ensemble mean have begun to pull back a bit on their previous trend of showing Rachel turning northeastward toward the Baja California peninsula, although there is still considerable spread in the track guidance by days 4 and 5. The updated NHC track forecast essentially maintains continuity with the previous forecast and is not too far from the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 19.1N 115.8W 55 KT 65 MPH 12H 27/1800Z 19.8N 116.3W 60 KT 70 MPH 24H 28/0600Z 20.7N 116.6W 65 KT 75 MPH 36H 28/1800Z 21.5N 116.8W 60 KT 70 MPH 48H 29/0600Z 21.9N 116.9W 50 KT 60 MPH 72H 30/0600Z 22.1N 117.0W 35 KT 40 MPH 96H 01/0600Z 21.5N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 02/0600Z 21.0N 118.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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