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Tropical Storm RACHEL Forecast Discussion Number 11
2014-09-27 04:51:45| National Hurricane Center (East Pacific)
Issued at 800 PM PDT FRI SEP 26 2014 000 WTPZ43 KNHC 270251 TCDEP3 TROPICAL STORM RACHEL DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 800 PM PDT FRI SEP 26 2014 Geostationary and microwave satellite imagery show a much improved structure for Rachel this evening. A pronounced curved band has developed and wrapped around the center of the cyclone, while a mid-level eye is seen in 2002Z AMSR-E, 2130Z AMSU, and 0127Z SSMIS microwave passes. Correspondingly, the Dvorak classifications from TAFB and SAB have jumped up to a 3.5. This supports a 55 kt intensity, which may be conservative as the CIMSS AMSU method suggests maximum sustained winds of about 75 kt. It appears likely that Rachel is responding to a reduction in the vertical shear, as it has now dropped below 10 kt. Rachel has about 24 to 36 hr of conducive environmental conditions remaining before the atmosphere that it moves into becomes quite dry and stable. In about three days, the vertical shear increases which should hasten the demise of this system. The NHC intensity prediction is based upon the IVCN multi-model ensemble through 48 hr and upon the HWRF and GFDL hurricane models after that time. The peak intensity indicated here is above that from the previous advisory due to the jump in the initial intensity. The aforementioned AMSU pass also provided some guidance from the CIRA size technique for the initial tropical-storm-force wind radii, which have been expanded outward some as a result. The forecast wind radii, however, are anticipated to not grow much, based upon a blend of the dynamical and climatological models. Rachel's center apparently reformed southwestward closer to the deep convection earlier today, as suggested by a late arriving WindSat microwave pass. While the uncertainty in the initial position is low, the current motion is a bit ambiguous due to the reformation. It is estimated that the cyclone's center is moving toward the west-northwest at around 10 kt, primarily due to steering imparted by a mid-level subtropical ridge to its northeast. A vigorous shortwave trough near California is anticipated to induce a break in the ridge and allow Rachel to turn toward the north-northwest at a slower rate of forward speed by Sunday. In about three days, a decaying Rachel will start meandering in the weak low-level flow west of Baja California. The NHC track forecast is based upon the TVCE multi-model ensemble, which shows substantial divergence in solutions late in the forecast period, and is slightly east of the track shown in the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 18.4N 115.3W 55 KT 65 MPH 12H 27/1200Z 19.1N 116.1W 60 KT 70 MPH 24H 28/0000Z 20.0N 116.4W 65 KT 75 MPH 36H 28/1200Z 20.9N 116.7W 65 KT 75 MPH 48H 29/0000Z 21.5N 116.9W 55 KT 65 MPH 72H 30/0000Z 22.1N 116.8W 40 KT 45 MPH 96H 01/0000Z 22.0N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 02/0000Z 21.5N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Landsea
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