What is dirty rain? What we know about Saharan dust and summer thunderstorms this week

Lianna Norman and Cheryl McCloud, USA TODAY NETWORK - Florida
·6 min read

Every Floridian knows that summer brings thunderstorms on an almost-daily basis, tropical storms and hurricanes. But this summer, Saharan dust is joining the mix to make “dirty rain” for some parts of Florida.

During the late spring, summer and early fall, bursts of dust from the Saharan Desert are picked up by wind and form a big mass of dry, dusty air that sits about a mile into the atmosphere at its lowest point.

This mass of dry, dusty air is called the Saharan Air Layer (SAL), and its activity ramps up from mid-June through mid-August, when it moves over the tropical North Atlantic Ocean every three to five days.

“During this peak period, it is common for individual SAL outbreaks to reach farther to the west — as far west as Florida, Central America and even Texas—and cover extensive areas of the Atlantic (sometimes as large as the lower 48 United States),” NOAA’s guide to the Saharan Air Layer says.

This layer of dust can be good for keeping the tropics calm during hurricane season, but the dust can also mix with summer rain to create “dirty rain.”

Here’s what dirty rain is and where in Florida dirty rain is expected this week.

What does Saharan dust mean for Florida?

“For Floridians, Saharan dust has helped quiet storm development in the Atlantic Ocean during the first half of the 2024 Atlantic hurricane season,” the Pensacola Journal reported on July 22.

“More good news? It should slightly drop temperatures over the next week or so.”

But while the temperature could cool, there will also be “dirty rain” for parts of Florida over the next day.

A tropical wave of showers and thunderstorms is expected to move northwest across the state through Tuesday. Because of the Saharan dust lingering nearby, the rain could leave a muddy residue behind.

And the dust isn’t expected to keep hurricanes at bay all season.

“The favorable conditions that yielded Beryl are likely to return at some point in August, and that will probably yield an extended burst of hurricane activity,” Dr. Ryan Truchelut, chief meteorologist at WeatherTiger, told TCPalm.

“WeatherTiger’s real-time forecast remains for around twice the amount of storm activity in a normal hurricane season.”

What is dirty rain?

Like Saharan Dust, “dirty rain” isn’t toxic or dangerous, but can irritate you if you have pre-existing respiratory issues. “Dirty rain” is just dust mixed with water and can leave a muddy residue behind on any exposed surfaces it falls on.

If you want to minimize the amount of mud or dust you inhale or have a pre-existing respiratory issue, just avoid spending a lot of time outside or wear a face mask if you’re out for an extended amount of time.

Will Pensacola be impacted? Meteorologists claim 'dirty rain' will hit Florida this week.

What is the dirty rain in Florida from?

The dirty rain that could fall in central and southwest Florida this week is from recent plumes of Saharan dust mixing with rain from a low pressure wave of storms in the tropics.

What is Florida's rain forecast this week? Rain chances increase

At least 2 to 4 inches of rain will fall over much of the Southeast states through the end of this week, according to AccuWeather. The rain is associated with air from the Gulf of Mexico and southwestern Atlantic moving over the Southeast.

Florida may be spared from some of the worst rains, but a tropical wave of low pressure is increasing the chance for showers through Tuesday.

"As the tropical wave approaches and moves northwestward across the state from Sunday to Tuesday, an uptick in the showers and thunderstorms will occur with the potential for some to bring flooding downpours, strong wind gusts and even waterspouts near the beaches," said Alex DaSilva, AccuWeather lead hurricane expert.

The tropical wave is not forecast to develop into a tropical depression or a named tropical storm.

Temperatures and rain expected today, Monday, July 22:

  • Pensacola: High 87. Storms will start off along the coast and offshore during the early morning hours with better storm coverage spreading inland through the afternoon. Showers and storms will be scattered to locally numerous across much of the area by Monday afternoon. Localized minor flooding will be possible,

  • Tallahassee: High 93. Another day of widespread showers and thunderstorms across the region. Storms will likely get another early start.

  • Jacksonville: High 85. Chances for showers and storms increase this afternoon and into the evening hours. Periods of heavy rainfall will be possible. Not everyone will get the rain. A heat advisory has been issued until 6 p.m. for parts of North and Northeast Florida. Heat index values up to 108 to 110 expected.

  • Daytona Beach: High 89. Increased chances of showers and storms through Tuesday. A few storms may be strong, especially from Orlando north. Wind gusts up to around 50 mph are possible, along with locally heavy rainfall up to 1-3 inches.

  • Melbourne: High 90. Band of dry air near Melbourne before sunrise forecast to move north. Disturbance will help to generate scattered to numerous showers and storms today. Lingering showers and storms will be possible through sunset, generally west of Orlando. Drier conditions will then prevail overnight.

  • Port St. Lucie: High 90. Expect scattered to numerous showers and storms today. Overnight, a few showers and storms will remain possible along the Treasure Coast toward morning.

  • West Palm Beach: High 85. A tropical wave will approach South Florida early this morning. Just over 2 inches of rain expected by this afternoon. Showers and storms could impact the East Coast metro areas beginning early this morning and continuing through the late morning hours.

  • Naples: High 90. Scattered to numerous thunderstorms will be possible this morning and afternoon. The strongest storms could produce gusty winds, frequent lightning, and heavy downpours. Localized flooding may become a concern today for areas that receive repeated rounds of heavy rainfall. A few waterspouts cannot be ruled out today across the local waters.

  • Fort Myers: High 91. Another typical Florida summer day in store, characterized by hot and humid conditions ending with showers and thunderstorms. Main concerns would be frequent lightning, localized heavy rainfall, and gusty winds. Storms will likely develop late afternoon over South Florida and move northwest through the evening.

  • Sarasota: High 92. A clash between Saharan dust in mid levels of the atmosphere with moisture in the lower levels could bring some stronger storms to the area today. Lightning, localized heavy rainfall, and gusty winds are all possible. The dust is expected to dissipate Monday into Tuesday. Scattered to numerous showers/storms are expected each day this week.

This article originally appeared on Florida Today: Dirty rain's Florida Saharan dust relationship. What to know