Already responsible for triggering significant flooding across Puerto Rico, Isaac threatens to cause similar problems across Hispaniola, Cuba and Jamaica into this weekend.
After moving through the Leeward Islands earlier this week and south of Puerto Rico on Thursday, Isaac was moving south of Hispaniola Friday with showers and squalls spreading into the island and across Puerto Rico.
The worst effects in terms of rain in these areas will occur through Saturday morning as tropical moisture is pumped in on the eastern flank of the storm.
Puerto Rico was being inundated by torrential rain and an outer spiral band from Isaac Friday. Some roads have been blocked by mudslides or flooded. At least one bridge was washed out along the southern part of the island.
San Juan, P.R. radar from 1:15 p.m. EDT, Friday, Aug. 24, 2012.
"Training-effect rain and thunderstorms were blasting Puerto Rico like a giant fire hose during Friday," Expert Senior Meteorologist Alex Sosnowski said.
Isaac will be in a favorable environment for strengthening with warm water and weak wind shear.
Isaac may strengthen into a Category 1 hurricane before it reaches Cuba on Saturday. However, as Isaac interacts with the higher terrain of Cuba on Saturday, it should weaken once again.
"We are likely to see more bands of intense, persistent rainfall set up on Hispaniola, Cuba and even for a time yet in Puerto Rico into the weekend," Sosnowski added.
AccuWeather Senior Meteorologist Dan Pydynowski expects 4-8 inches of rain to fall across Puerto Rico, Hispaniola and Cuba with the potential for 10 inches or more in the mountains.
Coastal flooding occurred near Duffs Bottom on the western end of Tortula, British Virgin Islands Thurs., Aug. 23, 2012. Image taken by Radi Hassan.
A westward shift in Isaac's track on Friday will likely spell more trouble for Jamaica than previously thought.
A total of 1 to 2 inches of rain will overspread the island into Saturday. Locally higher totals are a concern and could lead to flash flooding and mudslides, especially across eastern areas.
Additionally, tropical storm-force winds will lash the southern half of the Dominican Republic, Haiti and eastern Cuba through Saturday. Hurricane-force winds are also a threat along southwestern Haiti and eastern Cuba.
AccuWeather.com Meteorologist Steve Travis contributed to this article.
Smoke created hazy, orange views in Los Angeles on Saturday as the Sand Fire continued to rage less than 40 miles away from the city's downtown.
Conditions will continue to deteriorate across Hawaii this weekend as Darby delivers locally heavy rain and rough surf.
Dangerous heat will surge northward and send temperatures soaring across the northwestern United States during the final week of July.
Much of the eastern United States will continue to swelter with above-average temperatures into the end of the month.
Stifling heat has been baking the central United States but will finally ease across northern areas this weekend.
Lightning killed a teenager on Friday, the second teen lightning death in three days. With thunderstorms continuing to rattle several parts of the nation, more lives will be at risk.
North Carolina (1975)
Lightning killed 13 cows during a thunderstorm at Kenansville. Heavy rains elsewhere in the state forced the Tar River out of its banks at Greenville, causing 14 families to evacuate their homes.
New York (1975)
Severe thunderstorms in western and central NY: lightning struck a city park in Rochester injuring 12 children, all were playing on a metal jungle gym. One patrolman described the scene as if "someone threw a stick of dynamite in the middle of the crowd and it blew."
Southeastern MA (1990)
Torrential rains: Middleboro 7.20" Bridgewater 5.00" Tauton 4.33" Abington 3.05" Cars were stranded in high water in Fall River, MA.