Tropical Wave To Develop As It Moves West

Hurricanes Humberto and Imelda presented a rare case of how a hurricane can save the US from being impacted by a different hurricane, while diverting both hurricanes toward Bermuda. The pair had histories dating from mid-September to early October, but their DNA was embedded in a storm that ended up in northwestern Europe.

Humberto and Imelda came off Africa as a pair in the middle of September and slowly trekked across the Main Development Region for a week until Tropical Storm Humberto formed on September 24 several hundred miles east of the Leeward Islands.

By the 24th and 25th, the tropical wave that eventually spawned Imelda first brought widespread rainfall of 1 to 4 inches across Puerto Rico, with the heaviest totals being reported across the southern parts of the territory. No surprise that this heavy rainfall brought some flood and landslide reports across Puerto Rico highways, with one car being washed out with people still inside. At least one person was killed.

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As Humberto formed several hundred miles to the northeast, the wave that would become Imelda spread rain to Hispaniola. One person was killed and 5,000 homes were flooded in southwestern Haiti. Landslides and river flooding punished the Dominican Republic, where a bridge collapsed as a truck crossed, killing the driver in Yamasá. A satellite loop from the day can be seen here.

By September 26, Humberto had become a hurricane well to the northeast of Puerto Rico as pre-Imelda moved its drenching rains over Cuba and the Bahamas.

Flooding and landslides were reported in Cuba, where two people were killed.

The forecast for Imelda became extremely uncertain that day with many models pointing the future hurricane toward the Carolinas and others out to sea. For more on this days-long conversation, see our next section.

Humberto underwent rapid intensification later that day, with its maximum sustained winds jumping from 65 to 145 mph in only 24 hours. It then went on to become the second Category 5 hurricane in the Atlantic Basin so far this season.

Tropical Storm Imelda formed during the afternoon of Sept. 28 as the storm's center neared Andros Island and Nassau.

As Imelda moved through the Bahamas, a peak wind gust of 44 mph was clocked at Nassau and 38 mph at Freeport. Just over 2 inches of rain was reported at Over Yonder Cay, located about halfway between Nassau and Exuma.

Imelda turned to the right shortly after making it out of the northern Bahamas on September 29, and accelerated shortly after. Meanwhile, Humberto made its closest pass to Bermuda, passing just 265 miles southwest and west of the archipelago as a Category 3 with sustained winds of 115 mph. Impacts in Bermuda were fairly minimal.

The two storms began to strongly interact on September 30 as the storms neared their closest pass.

Unusually Tight Dance Of Hurricanes

The centers of Humberto and Imelda were separated by less than 500 miles, the closest any two Atlantic Basin hurricanes have been to each other in at least 59 years, according to WPLG-TV hurricane expert Michael Lowry.

Upper-level outflow winds from Imelda also increased wind shear over neighboring Humberto, as the satellite loop in a post on X from NOAA/CIRA below shows.

The interaction of two tropical systems — or low pressure areas in general — is known as the Fujiwhara effect. In this case, Humberto's close proximity saved the Southeast from a landfall from Imelda, halting its northward drift and instead pulling it east.

In the day ahead of Imelda's impacts in Bermuda, the Government of Bermuda announced L.F. Wade International Airport, the Causeway linking St. David's Island and Hamilton Parish, and all public schools were closed.

Hurricane Imelda raced through Bermuda early on the morning of Oct. 2 just days after Humberto brought breezy conditions. Both storms generated high surf, rip currents and some coastal flooding along parts of the East Coast.

Imelda's Extreme Forecast Challenges

The forecast for the system that eventually became Imelda was very uncertain.

Three distinct camps in computer model guidance developed: One that took Imelda into the Carolinas, a second that stalled the storm off the Southeast coast, and a third that took Imelda away from the Southeast and out to sea.

At the bookends of this forecast challenge were an unseasonably far south upper-level low that was forecast to dig into the Southeast and the Bermuda High to the east. In between these two, both Imelda and Humberto were set to trot a relatively narrow gap. Models had to get the strength and position of all four features and their interactions correct.

In just 48 hours from late on Sept. 26 — when the first cone of uncertainty was issued — to the evening of Sept. 28, the NHC forecast changed significantly from a potential landfalling hurricane in the Southeast U.S. to a hard east turn well before the storm could reach the coast, as the graphic below shows.

(More: How Imelda's Forecast Changed)

It turns out Imelda's slower northward progress, a weaker upper-level low and a stronger than initially forecast Humberto made an enormous difference in the track of Imelda. Humberto being stronger than expected allowed for the storm to help break down the Bermuda High, which would have steered Imelda into the Southeast.

The impacts between Imelda and Humberto were not one way. There was also a more subtle change in Humberto's intensity because Imelda ended up close enough to Humberto to impart a taxing, strong upper-level northwest wind, causing Humberto to weaken.

Humberto's 'Ghost' To Spawn 'Amy'

Humberto merged with a nearby cold front. While that frontal merger spells the end of Humberto, it wasn't the end of the story.

Some of Humberto's remnant energy triggered an intense North Atlantic storm that moved into the far north Atlantic, Ireland, the U.K. and parts of western Europe beginning October 3 with high winds and heavy rain.

The U.K. Met Office has named this "Storm Amy", their first storm of the 2025-26 season.

In fact, low pressure will plunge so rapidly that Storm Amy will likely meet the criteria for a bomb cyclone, a rapidly intensifying low pressure system typically responsible for destructive winds.