WTPZ42 KNHC 210840
TROPICAL STORM POLO DISCUSSION NUMBER 21
NWS NATIONAL HURRICANE CENTER MIAMI FL EP172014
200 AM PDT SUN SEP 21 2014
Polo has continued to be impacted by strong easterly wind shear of around 25 kt, which has severely weakened the associated convection. What little convection that does exist has been displaced into the western quadrant. A 0413 ASCAT-B overpass indicated several 33-kt wind vectors in the northeastern and southwestern quadrants. Since some undersampling is possible, the initial intensity is being maintained at 35 kt for this advisory, especially since some convective redevelopment could return during the remainder of the convective maximum period this morning while the cyclone is over SSTs near 28C.
Now that Polo's low and upper-level circulations are beginning to weaken and decouple, the cyclone has made a westward jog and the initial motion is now 285/06 kt. However, the track forecast and reasoning basically remain unchanged from the previous advisory. Polo is expected to continue to weaken and become more vertically shallow, being steered westward and eventually southwestward by a strengthening low- to mid-level ridge located to the north of the cyclone. The NHC forecast track is similar to the previous advisory track and TVCE multi-model consensus.
Strong easterly vertical wind shear is forecast to continue for the next 36 hours or so, which should cause Polo to continue to weaken. The cyclone will likely become a tropical depression later today, and degenerate into a remnant low on Monday, if not sooner. Although the remnant circulation will be moving back over warm water on Days 3 and 4, the surrounding airmass is expected to be dry and more stable, which should inhibit any persistent convective development from occurring.
Given that the size of Polo's wind field has decreased and that the cyclone is also now moving away from Baja California Sur, the Government of Mexico has discontinued the tropical storm watch for Baja California Sur.
FORECAST POSITIONS AND MAX WINDS
INIT 21/0900Z 21.6N 110.5W 35 KT 40 MPH 12H 21/1800Z 21.9N 111.7W 30 KT 35 MPH 24H 22/0600Z 22.1N 113.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 22/1800Z 22.0N 114.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 23/0600Z 21.5N 115.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 24/0600Z 20.3N 116.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 25/0600Z 19.0N 117.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 26/0600Z...DISSIPATED
$$ Forecaster Stewart