Tropical systems to unleash torrential downpours in northern Caribbean

Downpours will push westward across the northern islands of the Caribbean Sea, while a second tropical system, dubbed 99L, limps along farther to the east in the Atlantic.

Unsettled weather, similar to a tropical depression or a weak tropical storm, will affect areas from Leeward Islands to Puerto Rico, Hispaniola and the Bahamas early this week. However, this system is likely to remain poorly organized as it moves westward through Wednesday.

These islands will experience an pulse of drenching showers and locally gusty thunderstorms over a 12- to 36-hour period during the first part of this week.

The showers and thunderstorms may postpone some activities such as a day at the beach or boating adventure.

Beyond Wednesday, some of this moisture may feed into the general pattern of showers and thunderstorms and enhance rainfall and gusty storms along the southeastern coast of the United States.

On occasion, features such as this can transform into a potent tropical system. However, this risk is very low at this time.

99L may develop, track near Leewards later this week

A more organized batch of showers and thunderstorms, referred to as 99L, was located hundreds of miles farther east over the Central Atlantic.

When batches of thunderstorms in the Atlantic Ocean have the potential to become a tropical depression or storm, they are given a number between 90 and 99. The "L" designation refers to a system under investigation in the Atlantic.

"We have noticed an uptick in thunderstorms and some spin to the cloud cover on Monday," according to AccuWeather Hurricane Expert Dan Kottlowski.

"However, 99L is moving into a zone of dry air and strong wind shear over the next couple of days," Kottlowski said.

Wind shear is the changing of speed and direction of winds at different layers of the atmosphere. Strong wind shear can prevent tropical development or diminish the intensity of tropical storms and hurricanes.

Balancing these considerations, while 99L could become a tropical depression at any time, rapid strengthening seems unlikely in the short term.

It is likely 99L will take a general path just northeast of the Leeward Islands later this week.

If 99L remains weak, then it will drift more to the west. If 99L strengthens, then it is more likely to turn a bit toward the northwest.

"Should 99L survive the dry air and wind shear, it could strengthen later this week and this weekend," Kottlowski said.

A round of showers and thunderstorms associated with 99L can occur in the Leeward Islands on Thursday and Thursday night.

How extensive the rainfall is will depend on the exact track of the system.

Hundreds of miles farther west, Franklin will hit Mexico twice in the span of a few days this week.