For the first time in 2021, the National Hurricane Center issued a Special Tropical Weather Outlook (STWO) on Friday morning, indicating the potential for development of a low pressure system (Invest 90E) over the eastern Pacific. The Eastern Pacific hurricane season does not officially begin until May 15, but there is a significant chance that 90E could develop into a tropical depression by Monday. Pre-season tropical cyclogenesis in the eastern Pacific has been common in recent years, as three of the last four seasons have featured a tropical cyclone develop in the eastern Pacific prior to the official state date. Last season, in fact, had Tropical Depression One-E form on April 25, which was the record-earliest tropical cyclone in record on the basin. It should be noted that pre-season eastern Pacific tropical cyclone activity is not necessarily a harbinger of an active season in the basin, as last season finished with only four hurricanes and well-below average Accumulated Cyclone Energy (ACE).

Current Invest 90E Information

As of 18:00 UTC May 7, Invest 90E was located near 11.2°N 102.5°W. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1008 mb. In a Special Tropical Weather Outlook issued Friday morning at 8:00 a.m. PDT (11:00 a.m. EDT), the National Hurricane Center (NHC) gave 90E a 40% chance of development within 48 hours, and a 60% chance within five days. If 90E develops into a tropical cyclone with maximum 1-minute sustained winds of at least 39 mph, it would be named Andres. Shower and thunderstorm activity has decreased since this morning, but this is fairly typical for developing low pressure systems in their diurnal minimum period.

90E Forecast

90E has a relatively short window of marginally favorable conditions for development. The 18z Friday run of the GFS-based SHIPS model predicted that wind shear would be light for the next 36 hours (less than 10 knots), with sea surface temperatures warmer than 29°C (84.2°F), and 500-700 mb relative humidity values of around 65 percent. Wind shear will gradually increase beginning at 48 hours, while sea surface temperatures will decrease and 700-500 mb relative humidity values will decrease. Therefore, if tropical cyclogenesis does occur, it will most likely happen no later than Monday. Although the environment appears favorable, arguing against significant development is climatology, and none of the recent pre-season eastern Pacific tropical cyclones have gotten stronger than a low-end tropical storm. The 12z GFS and ECMWF global models agree, as both develop a weak closed low with 90E but do not show it becoming an organized tropical cyclone. 90E is expected to move relatively slowly west-northwest over the open eastern Pacific and will not pose a threat to land.