Tropical Storm Alvin Discussion Number 8
Wiki-Hurricanes Forecast Center
8:00 AM PDT Thu Jun 27 2019
Alvin has undergone some structural changes over the past few hours. Microwave imagery from around 10z showed the formation of an inner core and symmetric eye. This feature, however, was more ragged in a recent 14z microwave pass. The storm's presentation on conventional infrared imagery continues to be somewhat ragged, with a rather amorphous central dense overcast. The first frames of high-resolution visible imagery indicate that Alvin remains embedded in a stable low-level environment, which may explain the degradation in inner core organization since earlier this morning. Both SAB and TAFB gave intensity estimates of T3.0/45kt. UW-CIMSS ADT stands at T3.4/53kt. The initial intensity for this advisory has therefore been nudged upward to 50kt, which is in line with a peak wind barb of 46kt from an earlier ASCAT pass that had a hard time assessing the strength of a very small Alvin. This could be generous given trends in recent hours.
Alvin has about 12 hours left before upper-level winds begin to decrease and the storm crosses the 26C isotherm. Until that time, the environment could be favorable for some further development as indicated by the HWRF. One factor working against this scenario is the recent degradation in inner core quality. Given HWRF's high bias to date, I have opted not to indicate further strengthening, instead siding with the SHIPS and LGEM which show a steady state cyclone over the coming hours. Otherwise, dissipation has been moved forward to 72 hours, with degeneration prior to that. Alvin has been moving toward the west-northwest over the past few hours, and this trajectory should continue as it is steered by a mid-level ridge over northern Mexico. A turn toward the west is expected as the storm weakens and becomes embedded in the typical easterly trade wind flow across the East Pacific.
FORECAST MAX WINDS
INIT 27/1500Z 50 KT 60 MPH
12H 28/0000Z 50 KT 60 MPH
24H 28/1200Z 45 KT 50 MPH
36H 29/0000Z 35 KT 40 MPH
48H 29/1200Z 25 KT 30 MPH...POST-TROP/REMNT LOW