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TROPICAL STORM JIMENA DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132015
800 AM PDT THU AUG 27 2015

Jimena is steadily becoming better organized with deep convection
persisting near the center and more pronounced banding developing
around the circulation.  The initial intensity is 40 kt based on
Dvorak estimates of T2.5/35 kt from TAFB and T3.0/45 kt from SAB.
Embedded in an environment of low shear, high moisture, and very
warm ocean water, Jimena should have no problems continuing to
intensify.  In fact, rapid intensification (RI) is a distinct
possibility during the next 24 hours.  A low-level inner core ring
was noted in the 37-GHz channel of a 0946 UTC GPM microwave pass,
and the SHIPS RI index is showing a 1 in 3 chance of a 30-kt
intensity change during the next 24 hours.  Therefore, the NHC
intensity forecast shows Jimena becoming a hurricane on Friday.
After 24 hours, the overall environment should remain favorable for
strengthening, and Jimena is forecast to be a major hurricane from
day 3 through day 5.  The updated NHC intensity forecast is a
little higher than the IVCN intensity consensus and shows a bit
more strengthening than the previous forecast through 96 hours.

The storm has been moving quickly west-northwestward with a 12-hour
motion of 285/15 kt.  A strong deep-layer ridge extends from
northwestern Mexico to just east of the Hawaiian Islands, and this
feature should steer Jimena generally westward during the next 48
hours.  A weakness is expected to develop in the ridge by 72 hours,
which should turn the cyclone west-northwestward through day 5.  The
track guidance has shifted slightly southward during the first 48
hours, and the updated NHC track forecast follows suit but still
lies a little north of the model consensus.  The updated forecast is
largely unchanged from the previous one after 48 hours.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 12.4N 117.7W   40 KT  45 MPH
 12H  28/0000Z 12.7N 119.7W   50 KT  60 MPH
 24H  28/1200Z 13.0N 122.1W   65 KT  75 MPH
 36H  29/0000Z 13.1N 124.2W   80 KT  90 MPH
 48H  29/1200Z 13.1N 126.1W   90 KT 105 MPH
 72H  30/1200Z 13.9N 129.6W  105 KT 120 MPH
 96H  31/1200Z 15.5N 134.0W  115 KT 130 MPH
120H  01/1200Z 17.0N 137.5W  115 KT 130 MPH

$$
Forecaster Berg

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