A pulse of tropical energy hit the Atlantic basin this week, with a possible hurricane brewing near Africa and a sloppy wave in the Caribbean threatening South Florida’s long holiday weekend.
National Hurricane Center forecasters predicted Thursday a swirl of thunderstorms hundreds of miles east-southeast of the Cabo Verde Islands would become Tropical Storm Florence before building to hurricane strength by Sunday.
The system is not forecast to affect the U.S., but if predictions hold true it will be the sixth named storm of the season and the third hurricane, following the short-lived July hurricanes Beryl and Chris.
Of more concern to National Weather Service meteorologists in Miami is a tropical wave near Puerto Rico that could bring heavy rain this weekend to areas from the Treasure Coast to the Keys. The hurricane center gave the disturbance a 10 percent chance of developing into a tropical cyclone during the next five days as it moves into the warm waters of the Gulf of Mexico.
After Florence, the next name on the 2018 storm list is Gordon.
Meteorologist James Thomas said more than 2 inches of rain are possible through Monday from the wave, but cautioned that forecast models differ on timing and location with one taking it through the Florida Straits and another moving it north of the Straits.
“There’s a rather wet pattern setting up with the showers and storms coming really at any part of the day,” Thomas said. “I wouldn’t say there will be an overall washout Saturday and Sunday, but that could come Monday and Tuesday.”
Rain chances increase from 40 percent Friday to 50 percent Saturday and 60 percent Monday through Wednesday.
Hazards, including a slight risk for flooding and a moderate risk for rip currents, are expected Sunday through Tuesday. A high risk for lightning is also in the forecast for the same time period.
“If anything, it will be Monday and Tuesday we keep our eyes open for flooding,” Thomas said. “Sunday the rain will be more hit or miss.”
If the wave makes it into the Gulf of Mexico, it will have plenty of warm water to “feast on,” said Jeff Masters, co-founder of Weather Underground.
At 86 degrees, the Gulf is running 1.8 degrees warmer than normal.
“The total amount of heat energy in the Gulf right now is at near-record levels for this time of year — similar to last year’s levels, and much higher than observed during the awful hurricane season of 2005,” Masters wrote in his Cat 6 blog.
No one is predicting a repeat of 2005. The Climate Prediction Center and Colorado State University are both forecasting below normal hurricane activity this year, but peak hurricane season lasts through mid-October
“Last year was all about September,” said CSU lead hurricane forecaster Phil Klotzbach. “We don’t expect another 2017, but that’s not to say we won’t get something.”
Helping push the wave into South Florida is a strong clockwise-spinning Bermuda High. But a separate circulation center closer to the Azores is what’s forecast to send the potential tropical cyclone near the Cabo Verde Islands northwest into the Central Atlantic, said AccuWeather hurricane expert Dan Kottlowski.
Two more tropical waves that are forecast to leave the coast of Africa next week would likely follow the same path.
“The deeper the system gets, the more likely it will be drawn into that stronger high over the Azores,” Kottlowski said.
Forecasters will also be watching for the storm-inciting Madden-Julian Oscillation, or MJO, in the coming weeks it makes its way into the Atlantic. The MJO is a global player in the tropics — an eastward moving grouping of clouds, showers and winds that traverses the planet and returns to its starting point in 30 to 60 days
Tropical activity this storm season has been normal in number of named storms and number of hurricanes. But Chris and Beryl maintained hurricane strength for just 3.25 days, when the average for this time in the season is six days. The Accumulated Cyclone Energy — a measure of the strength and longevity of a storm — is 17.5 this season when the normal is 28.7.