|Tropical Depression Four-E||Winds: 30 kt|
|Pressure: 1006 mbar|
|Advisory 1 / 2:00 PM PDT Friday, July 12, 2019|
Somewhat surprisingly, a new tropical depression has formed over the East Pacific. Visible satellite imagery shows an area of deep convection has persisted today, weighted west of the low-level circulation as a result of strong northeasterly wind shear. Based on low-level cloud motions, there was some doubt whether a well-defined surface center existed. However, a 1632z ASCAT pass showed that one had indeed formed. The same pass showed winds just shy of 30kt, which is the initial intensity used for this advisory.
Upper-level winds on the order of 15-20kt are not expected to slacken at all during the five day forecast period. That being said, ocean temperatures above 26C and mid-level relative humidity values above 60 percent should allow maintenance of the nascent cyclone for the next 24 hours or so. The complicated question is whether intensification is possible during that time. The SHIPS and the LGEM both bring Four-E to tropical storm strength within 12 hours. They are on an island though, with the HWRF, HMON, ECMWF, and GFS all struggling to even portray a well-defined circulation, much less a tropical storm. Given the persistence of the deep convection, it would not be too surprising if a later ASCAT pass identified tropical storm-force winds. This, obviously, is dependent on the instrument hitting the tropical cyclone. With confidence so slow, it seems prudent to maintain a steady-state storm in the short term. Degeneration is expected in 36 hours, but this is probably generous as far as the cyclone's lifespan is concerned.
Four-E is moving on a general west-northwest path, and this trajectory should continue over the next few days. After 36 hours, the remnants of the storm may turn toward west, embedded within the low-level easterly trade wind flow across the East Pacific.
FORECAST MAX WINDS
INIT 12/2100Z 30 KT 35 MPH
12H 13/0600Z 30 KT 35 MPH
24H 13/1800Z 30 KT 35 MPH
36H 14/0600Z 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 14/1800Z 25 KT 30 MPH...POST-TROP/REMNT LOW72H 15/1800Z..DISSIPATED