056 
 WTPZ42 KNHC 210840
 TCDEP2
 
 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