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WTPZ42 KNHC 210840
TCDEP2

TROPICAL STORM LOWELL DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL EP122014
200 AM PDT THU AUG 21 2014

Lowell continues to exhibit a rather large, but ragged eye in microwave and geostationary satellite imagery. The latest Dvorak intensity estimates are 55 kt from SAB and 65 kt from TAFB. A couple of recent ASCAT passes shows a large area of 50 to 55 kt winds. Based on a blend of the satellite estimates and the ASCAT data the initial wind speed is increased to 60 kt. Although not explicitly shown in the official forecast, Lowell could become a hurricane during the next 6 to 12 hours while it remains over 26 degree Celsius water and in a low-shear environment. After that time, the shear is expected to remain low, but the cyclone will be moving over progressively cooler waters and into a more stable air mass that should cause weakening. Given the large size of Lowell's wind field, the rate of weakening is likely to be slower than the typical spin down of eastern Pacific tropical cyclones that move over cool water. In fact, Lowell is likely to become a convective-free post-tropical cyclone with gale-force winds in a few days.

The initial motion estimate is 315/3. A mid- to upper-level trough extending southwestward from southern California will weaken and move eastward today. This will allow the subtropical ridge to the north and east of Lowell to rebuild, which will result in a slightly faster northwestward motion during the next several days. The track guidance is in good agreement during the first 2 to 3 days, and the NHC track is near the middle of the tightly clustered model envelope during that time. Later in the period the spread of the models increases, but for now the NHC track will remain near the model consensus at days 4 and 5.



FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 19.7N 121.9W 60 KT 70 MPH 12H 21/1800Z 20.3N 122.5W 60 KT 70 MPH 24H 22/0600Z 21.3N 123.6W 55 KT 65 MPH 36H 22/1800Z 22.3N 124.8W 50 KT 60 MPH 48H 23/0600Z 23.4N 126.3W 45 KT 50 MPH 72H 24/0600Z 25.3N 129.0W 35 KT 40 MPH...POST-TROPICAL 96H 25/0600Z 27.0N 131.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/0600Z 28.3N 134.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$ Forecaster Brown



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