Tropical Storm Alvin Discussion Number 5
Wiki-Hurricanes Forecast Center
2:00 PM PDT Wed Jun 26 2019
After a fruitful diurnal maximum this morning, Alvin has adopted its new convective structure, unfurling its rainbands and presenting good radial anticyclonic outflow as evidenced by the transverse cirrus. Microwave and scattermoeter data have confirmed that the low-level center and convection are now fully aligned. A new burst of activity has been formenting at the center since about 18z with fresh -80C cloud tops. Convection continues to grow outwards, and banding is organized in all quadrants. An ASCAT-C scatterometer pass at 1629z showed just one gridpoint of 40 kt winds near the center. This value was flagged but is believable. Alvin is a very small system, and gale-force were not sampled more than 20 miles outward. There is good agreement between the satellite wind data and both infrared and microwave intensity metrics, so the intensity for Alvin is for this advisory remains at 40 kt in support of their data.
Given the current structural organization and alignment of Alvin's circulation as noted in the last advisory, the tropical storm appears to be well-equipped to reap currently favorable environmental parameters characterized by low wind shear and deep-layer temperature differences in excess of 80C between the sea surface and 200 hPa pressure level. ECMWF-IFS ensembles have won the day in terms of showing this morning's southwestward dip, though now most track guidance has come into agreement over the forecast track with the exeception of HWRF which continues to depict a minimal hurricane on a more poleward track. HWRF and HMON both show Alvin intensifying into a borderline hurricanes, and SHIPS guidance suggests that the more zonal consensus track regimes do indeed support substantial intensification over the next two or so days. The intensity forecast has been raised in the short-term to reflect these changes. Track guidance in general still shows the same steering patterns with more agreement between 12z global models, so no change to the track philosophy is introduced with this advisory.
FORECAST MAX WINDS
INIT 26/2100Z 40 KT 45 MPH
12H 27/0600Z 50 KT 60 MPH
24H 27/1800Z 45 KT 50 MPH
36H 28/0600Z 40 KT 45 MPH
48H 28/1800Z 30 KT 35 MPH
72H 29/1800Z 20 KT 25 MPH...POST-TROP/REMNT LOW