Subtropical Storm Andrea Forms in the Atlantic; Dangerous Severe Weather Outbreak Continues in OK, TX

May 20, 2019, 6:50 PM EDT

Above: Subtropical Storm Andrea as seen by the GOES-16 satellite at 1:50 pm EDT May 20, 2019. Image credit: NOAA/RAMMB.

Data from an Air Force hurricane hunter aircraft has confirmed that the 2019 Atlantic hurricane season is off to an early start: Subtropical Storm Andrea formed in the waters a few hundred miles southwest of Bermuda at 6pm EDT Monday evening. Andrea’s formation date of May 20 comes twelve days before the official June 1 start of the Atlantic hurricane season.

Satellite loops on Monday evening showed that Andrea had a modest area of heavy thunderstorms to the northeast of its center; these thunderstorms had grown substantially in intensity and areal coverage, but were well removed from the center of circulation, something that is characteristic of a subtropical cyclone. The hurricane hunters recorded sustained winds of minimal tropical storm-force, 40 mph.

Wind shear over Andrea was a high 25 knots on Monday evening, and sea surface temperatures (SSTs) were near 24.5°C (76°F), conditions that are marginal for development. The atmosphere Andrea was embedded was moist, with a relative humidity at mid-levels of the atmosphere of 60%.

Forecast for Andrea

Andrea was headed north at 14 mph on Monday evening, and will turn to the northeast and then east on Tuesday and Wednesday. This track will keep the storm to the southwest of Bermuda.

As Andrea moves north, it will encounter cooler waters, which will limit intensification and make it difficult for the subtropical storm to make the transition to a tropical storm. By Wednesday morning, Andrea is expected to merge with a cold front and dissipate, before reaching Bermuda. In their 6:30 pm EDT Monday wind probability forecast, NHC was giving only a 7% chance that Bermuda would see sustained tropical storm-force winds of 39 mph or greater from Andrea.

According to CSU hurricane scientist Phil Klotzbach, the Atlantic has now had named storms form prior to June 1 in five consecutive years: 2015-2019. This breaks the old record of named storm formations prior to June 1 in four consecutive years, set in 1951-1954. Last year, Subtropical Storm Alberto formed on May 25. Andrea is the type of weak and short-lived storm that could well have been missed getting named in the days before satellite imagery was available in the Atlantic.

Damaging tornadoes and flooding still a threat for Oklahoma on Monday night

A high risk for severe weather was still in place Monday evening across much of Oklahoma and parts of northwest Texas, as discussed in detail in our last post. As of 7 pm EDT Monday, nine tornadoes had already been reported, including one that struck near the town of Mangum, OK, around 5 PM CDT. Intense thunderstorms were marching across the area, sliding northeast along a SW-to-NE-oriented front. As the front sags slowly southeastward, supercells are likely to continue moving along it, possibly generating multiple strong tornadoes. Other tornadic storms may form ahead of the line in southwest and south-central Oklahoma. Training of cells along the slow-moving boundary could lead to a serious flash flood threat Monday night. Very late Monday night, an intense squall line will rip from west to east across Oklahoma with winds that could top 80 mph in some spots.

Bob Henson, who is currently at SPC in Oklahoma, wrote the tornado section of this post.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995, and flew with the NOAA Hurricane Hunters from 1986-1990.

jeff.masters@weather.com

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