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Pre-season tropical or subtropical system could form late week and bring flooding threat to parts of the Caribbean

From The Weather Channel

By Linda Lam
Story Highlights

An area of low pressure may develop in the southwestern Atlantic late this week or into the weekend.

Regardless of development, heavy rainfall will bring the threat of flooding from Puerto Rico to eastern Cuba.

May has just begun but there are already signs something may be brewing in the tropics later this week.

Although the Atlantic hurricane season technically doesn’t start until June 1, tropical and subtropical systems can develop before then.

Just last year, in 2017, Tropical Storm Arlene formed in April in the North Atlantic, and in May 2106, Bonnie impacted the Southeast U.S. Coast.

This week, the area that will be monitored closely for possible tropical or subtropical development will be the southwestern Atlantic Ocean. According Dr. Rick Knabb, hurricane expert at The Weather Channel, of the six tropical storms that have developed in the Atlantic in May since 2007, all but one formed between the Carolinas and the Bahamas, so this is an area that warrants attention.

Computer model depiction of the area to watch for possible tropical or subtropical development late week.

Some computer models suggest that an upper-level area of low pressure will form late this week just north of the Caribbean, most likely between Puerto Rico, Hispaniola, Cuba and the Bahamas.

Showers and thunderstorms are expected to develop associated with this system. An area of low pressure along with persistent shower and thunderstorms are two of the ingredients necessary for tropical or subtropical development.

Warm water temperatures, typically around 80 degrees or higher, provide warm, moist air needed to support tropical cyclone development. Water temperatures near Puerto Rico, Hispaniola and Cuba are generally warm enough to support development.

Odds appear low at this time, but there is a chance that this system could develop over the weekend into a tropical or subtropical depression or storm. It could become the first named storm of the 2018 Atlantic hurricane season: Alberto.

Even if a tropical or subtropical system does not develop, there will be locally heavy rainfall in portions of Puerto Rico, Dominican Republic, Haiti and eastern Cuba.

Widespread rainfall totals of greater than 3 inches are possible from Puerto Rico into eastern Cuba, with locally more than 5 inches expected. Heavy rainfall could lead to flash flooding and mudslides.

This potential system is expected to move westward or northwestward toward the Southeast U.S. Coast this weekend into early next week. It’s not anticipated to be a strong system, but it could enhance moisture near coast.

However, it is too early for details on possible impacts so check weather.com for updates.

Difference Between Subtropical and Tropical Storms

A subtropical depression or storm exhibits features of both tropical and non-tropical systems, with a broad wind field, no cold or warm fronts and generally, low-topped thunderstorms spaced some distance from the center.

Subtropical cyclones typically are associated with upper-level lows and have colder temperatures aloft. Tropical cyclones are fully warm-core and upper-level high pressure systems overhead help facilitate intensification.

Because of this hybrid nature, the National Hurricane Center still issues advisories and forecasts for subtropical depressions and storms and assigns a number or name.

Occasionally, if thunderstorms cluster close enough and persist near the center, latent heat given off aloft from the thunderstorms can warm the air enough to allow the system to become fully tropical.

When that happens, the wind field will tighten closer to the center, opening the door to further intensification.

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.

IMAGES:

Rainfall Forecast Locally higher rainfall amounts are possible.

Current Water Temperatures

Computer model depiction of the area to watch for possible tropical or subtropical development late week.

For more on this story go to: https://weather.com/storms/hurricane/news/2018-05-01-pre-season-tropical-subtropical-system-caribbean-heavy-rain

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