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Tropical Storm Alvin Discussion Number 6

Wiki-Hurricanes Forecast Center

8:00 PM PDT Wed Jun 26 2019

Alvin has changed little in organization tonight. The satellite presentation is characterized by a somewhat-defined central dense overcast, with a ragged spiral band extending to the west and north. Upper-level outflow is great in all directions. There is a wide range in satellite intensity estimates this evening, with SAB having fallen from T3.0/45kt at 18z to T2.5/35kt at 0z. CIMSS ADT came in at T3.3/51kt. Microwave satellites are not suggestive of any defined inner core, so it would likely be premature to give weight to that latter estimate. The intensity is therefore held at 40kt on the back of the earlier ASCAT pass and closest to the SAB estimate.

At face value in the SHIPS file, the environment looks quite favorable for Alvin, with wind shear under 10kt, ocean temperatures around 28C, and mid-level relative humidity values around 60 percent for the next 24-36 hours. However, conventional satellite imagery shows a large mass of lower-level dry air in the vicinity of Alvin, which appears to already be having some impact. Despite this, both the SHIPS and LGEM show the storm intensifying another 10-15kt over the next day or so. The HWRF goes even farther and forecasts a hurricane by morning, ultimately peaking Alvin on the cusp of major intensity. Obviously, this is an outlier solution, and the HWRF continues to be discounted in my forecasts. The updated forecast looks a lot like the previous one.

Alvin has moved south of due west today under the influence of a stronger-than-forecast mid-level ridge across Mexico and the eastern Pacific. A curve back toward the west and west-northwest is expected as Alvin rounds the periphery of this ridge. A turn toward the west still appears plausible after the storm degenerates in 3 days or so.

FORECAST MAX WINDS

INIT 27/0300Z 40 KT 45 MPH

12H 27/1200Z 45 KT 50 MPH

24H 28/0000Z 45 KT 50 MPH

36H 28/1200Z 40 KT 45 MPH

48H 29/0000Z 30 KT 35 MPH

72H 30/0000Z 20 KT 25 MPH...POST-TROP/REMNT LOW

96H 01/0000Z...DISSIPATED

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