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Tropical Storm LOWELL Forecast Discussion

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WTPZ42 KNHC 200840

200 AM PDT WED AUG 20 2014

The large tropical storm is maintaining its strength tonight.
Curved convective bands remain well organized on the south side
of the circulation, but deep convection is thin to the north of the
center.  The initial intensity is kept at 45 kt, in agreement with
the Dvorak estimates from TAFB and SAB.  Lowell is currently over
27 C waters, and in an atmosphere of fairly low shear and high
moisture.  Since the storm is expected to remain in these favorable
conditions for another 36 hours, some strengthening is forecast.
Beyond that time, however, Lowell will be moving over waters cooler
than 26 C and into a drier and more stable air mass.  These
environmental conditions should cause the cyclone to gradually lose
strength.  The NHC forecast is similar to the previous one, and now
calls for Lowell to weaken to a remnant low by 96 hours.

Lowell has wobbled to the west recently, but a 12-h initial motion
estimate is northwestward at about 4 kt.  The track forecast
reasoning is unchanged from the previous advisories.  A mid- to
upper-level low over southern California has produced a substantial
weakness in the subtropical ridge and should cause Lowell to move
slowly northwestward to north-northwestward during the next day or
so.  The upper low is expected to move northeastward and weaken
late Thursday or Friday, allowing the subtropical ridge to build to
the north of the storm.  This pattern change should cause Lowell to
speed up and gradually turn west-northwestward.  The track guidance
has shifted a little to the west this cycle, and the NHC forecast
is adjusted slightly in that direction.

A pair of altimeter passes around 0400 UTC provided excellent sea
height data for Lowell; therefore, there is high confidence in the
12-ft sea radii for this advisory.


INIT  20/0900Z 18.7N 121.0W   45 KT  50 MPH
 12H  20/1800Z 19.1N 121.4W   50 KT  60 MPH
 24H  21/0600Z 19.8N 121.9W   50 KT  60 MPH
 36H  21/1800Z 20.5N 122.5W   50 KT  60 MPH
 48H  22/0600Z 21.6N 123.6W   45 KT  50 MPH
 72H  23/0600Z 24.0N 126.3W   40 KT  45 MPH
 96H  24/0600Z 26.0N 129.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  25/0600Z 27.0N 131.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

Forecaster Cangialosi

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Page last modified: Wednesday, 20-Aug-2014 08:41:04 UTC