Above: GeoColor satellite image of Invest 90E at 1915Z (3:15 pm EDT) Friday, April 24, 2020. (tropicaltidbits.com)
An area of disturbed weather gaining structure in the Northeast Pacific several hundred miles south of Cabo San Lucas, Mexico, is likely to become the earliest-in-the-spring tropical cyclone ever confirmed in the Eastern Pacific basin, where satellite-based records go back to 1970. In a tropical weather outlook issued at 8 am EDT Friday, the NOAA/NWS National Hurricane Center raised the odds to 80% that the system known as Invest 90E will become at least a tropical depression by Sunday. Those odds persisted in the 2 pm EDT update.
The Eastern Pacific hurricane season got off to a record-early start in 2017, when Tropical Storm Adrian formed on May 9. The previous earliest appearance of a named storm in the Eastern Pacific since reliable satellite records began in 1970 was on May 12, 1990, when Tropical Storm Alma got its start. Three other systems got their start on May 13, according to NOAA’s Historical Hurricane Tracks website.
The earliest tropical cyclone in the Central Pacific was Hurricane Pali, which formed on January 11, 2016. Pali benefited from unusually warm SSTs related to an intense El Niño event. (Arguably, Pali was a laggard storm from the 2015 season rather than an early storm in the 2016 season.)
Satellite imagery from Thursday night into Friday made it clear that Invest 90E was steadily organizing. Wind shear is light (less than 10 knots), which has allowed prominent upper-level outflow to develop to the north of 90E, helping to ventilate the system. Upper-level cross sections show that the broad center of 90E is nearly vertical, which also paves the way for potential strengthening. Some spin was evident in the overall circulation.
A broad swath of convection (showers and thunderstorms), some of it quite strong, developed on Thursday night. The convection waned somewhat Friday morning, but a new arc of thunderstorms was building Friday afternoon on the north side of 90E’s elongated center.
Forecast for 90E
There is ample warm water for 90E to develop, with sea surface temperatures of 27-28°C (81-82°F) running about 0.5 to 1°C above average. However, much cooler water is lurking just to the north, as is much stronger wind shear. If 90E does develop, it will be moving toward these highly unfavorable conditions, so any tropical cyclone emerging from 90E would likely dissipate by Monday, long before it had a chance to affect any land areas.
Computer models caught the potential for 90E several days in advance. By Thursday, a majority of the GFS and European model ensemble members were calling for 90E to develop into a tropical cyclone. Models can be a bit overeager to develop Eastern Pacific disturbances from the Intertropical Convergence Zone during the late winter and early spring. Before accepting such predictions at face value, it’s good to keep a climatological perspective in mind—but this time it appears the models were on to something.
That said, model guidance is unified on 90E becoming no more than a minimal tropical storm (if that) before it dissipates several days from now.
Jeff Masters: Is the Eastern Pacific hurricane season starting earlier?
WU co-founder and Cat 6 founder Dr. Jeff Masters provided his thoughts below on whether human-caused climate change might be at work in the development of 90E.
“With a record-early start to the season in 2017, and another potential record early start this year, the question naturally arises—is the Eastern Pacific hurricane season starting earlier due to climate change?
“We might expect that hurricane season will start earlier and end later in coming decades, due to warming of the oceans allowing more storms to form when ocean temperatures are marginally warm for tropical cyclone formation. However, hurricane genesis also requires low wind shear, high levels of moisture at mid-levels of the atmosphere, and something to get the low-level atmosphere rotating. In some ocean basins, climate change may inhibit early-season genesis events by decreasing these other factors needed for a hurricane to get started.
“There has not been any research published thus far showing a change in the length of the Eastern Pacific hurricane season. In 2017, CSU hurricane scientist Phil Klotzbach tweeted a plot of Eastern Pacific hurricane season start dates showing no trend in the start date since satellite data became available in 1970. A 2015 study of how climate change might be expected to influence season length in climate models (led by MIT’s John Dwyer) yielded mixed results for the Eastern Pacific, depending upon which model was used to simulate hurricane activity. Most of the models—but not all—projected an increase in the length of the Eastern Pacific hurricane season in a future warmer climate.
“The Atlantic hurricane season does appear to be getting longer in the region south of 30°N and east of 75°W, according to a 2008 paper by Dr. James Kossin of the University of Wisconsin in Geophysical Research Letters titled, "Is the North Atlantic hurricane season getting longer?" A 2016 analysis by Dr. Ryan Truchelut of WeatherTiger also supported this idea. However, Juliana Karloski and Clark Evans of the University of Wisconsin-Milwaukee found no trend in tropical cyclone formation dates when looking at the entire Atlantic, for the period 1979–2014.
“In summary, we don’t yet know if climate change is leading to an increase in Eastern Pacific tropical cyclone activity, and will have to wait for another decade or so of data to see.”
Dr. Jeff Masters contributed to this post.
