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Tropical Depression Gilma Discussion Number 7

Wiki-Hurricanes Forecast Center

8:00 AM PDT Sat Jul 28 2018

The effects of strong westerly shear imparted on Gilma from an expansive upper-level shortwave trough over the northeastern Pacific remains evident this morning as the tropical depression maintains an exposed but well-defined center of circulation with convection displaced southeast of the center. However, convective activity has increased during the overnight hours and now appears slightly more organized despite remaining removed from the low-level center. SAB estimated T2.0/30kt for a current intensity while TAFB analyzed T1.5/25kt. UW-CIMSS ADT indicated a marginal tropical storm with T2.5/35kt as the assessed strength. Although we do not have any recent clean scatterometer passes of GIlma, peripheral readings from ASCAT and OSCAT do not support gale-force winds. On this basis, given some nightly improvement, the initial intensity for GIlma has been increased to 30 kt.

According to scatterometer data, Gilma is somewhat entangled with the ITCZ and has not made much progress separating itself from the ITCZ with marginal beta drift given the storm's intensity. Thus, low to mid-level ridging over much of the northern Pacific and western United States is keeping the storm on a westerly path which should continue out to dissipation. Nothing new to introduce into the intensity forecast as wind shear is expected to remain high if not increase, and Gilma is expected to slowly taper off before degenerating into a remnant low in about 1-2 days before dissipating in 3-4 days. This slow weakening process could occur sooner if Gilma is unable to develop convection. No threat to Hawaii is assessed.

FORECAST POSITIONS AND MAX WINDS

INIT 28/1500Z 30 KT 35 MPH

12H 29/0000Z 25 KT 30 MPH

24H 29/1200Z 25 KT 30 MPH

36H 30/0000Z 25 KT 30 MPH

48H 30/1200Z 25 KT 30 MPH...POST-TROP/REMNT LOW

72H 31/1200Z 20 KT 25 MPH...POST-TROP/REMNT LOW

96H 01/1200Z...DISSIPATED