El Niño fuels burst of storms in the Pacific, with more to come

The Pacific Ocean has become a storm-spinning machine.

On Tuesday, short-lived Tropical Storm Julio marked the 10th named east Pacific storm so far this year — about 10 days earlier than normal. Three or four more storms are possible by the second week of September. That would put the basin just shy of its yearly norm of 15, with three months still remaining in hurricane season, which lasts through Nov. 30.

Cyclones in the central Pacific waters near Hawaii — between 140 degrees west longitude and the international date line — have been more energetic this year than storms in the entire Atlantic Ocean.

A big reason is El Niño.

This year, El Niño is “becoming so dominant” that it is “drowning out” another key weather factor, the Madden-Julian Oscillation, the National Hurricane Center said. The MJO is an area of thunderstorms circumnavigating the tropics, and typically central and east Pacific tropical cyclone activity ebbs and flows every two to six weeks due to those storms. But in recent months, record-warm ocean temperatures fueled by El Niño are supporting the nearly nonstop thunderstorms that provide the first key ingredient for potential tropical cyclones.

The Pacific “hot spot” will continue through early September, the center said, as El Niño’s imprint on the tropics holds steady. Most tropical storms and hurricanes will probably stay far away from land, but both Hawaii and California are positioned to experience potential impacts.

Here’s what meteorologists are monitoring for the rest of the season:

On Tuesday, tropical storm Julio and former tropical storm Iselle danced near each other before merging west of Cabo. California is forecast to see remnant moisture from these systems late Thursday and Friday, with increased cloud cover and a chance of rain.

There was a less than 10% chance of a tenth of an inch of rain in the Bay Area, but even a few drops would be rare for August. The Sierra has a better chance of rain — a tenth to a quarter-inch — as well as isolated thunderstorms. Isolated downpours may cause flash flooding.

In coastal Southern California, a beach hazards statement is in effect for dangerous rip currents and waves up to 7 feet generated by Iselle.

The hurricane center is monitoring another soon-to-be named system that may take a similar track to Iselle next week. There’s a chance that storm reaches hurricane strength and injects more moisture into the atmosphere than Iselle, further raising the potential for rain and thunderstorms in California.

El Niño has warmed tropical Pacific waters to record levels and created favorable conditions for storms when wind shear — changes in wind direction or speed with height — weakens. Above-normal tropical cyclone activity is expected through October. There may be weeks with no storms and some weeks with multiple, said Nick Novella, a meteorologist at the Climate Prediction Center.

While storms will be frequent, there may be too many cooks in the kitchen.

Weak storms in close proximity can interfere with one another and limit powerful hurricanes from forming. That happened when Julio was absorbed into Iselle and prevented it from becoming as strong as the hurricane center initially predicted.

If storms happen in the same area in succession, cool water churned up by the prior storm limits the heat energy needed for the next one. However, these “cold wakes” are shrinking in a warming climate, research shows.

While the water is too cold to support a full-blown hurricane near California, tropical cyclones can remain potent even after wind speeds fall below hurricane criteria. Tropical Storm Hilary in August 2023 brought heavy rain and flooding to parts of Southern California during an El Niño.

A Hilary repeat is unlikely, but that kind of impact is most common in September and October when El Niño is present. El Niño-warmed water near Baja can allow hurricanes to survive farther north than during a typical year.

The window is open in September and October as the semi-permanent summertime high-pressure system over the Four Corners begins to break down, and hurricanes more easily move north instead of west out to the open sea.

“There is growing potential for one of these tropical storms or hurricanes to make a right hook toward California,” Daniel Swain, a climate scientist at UC Agriculture and Natural Resources, said in an online presentation.

Though the probability of a direct landfall is low, “a far more likely outcome is that a weakening remnant (low-pressure system) brings a significant amount of moisture and potentially some large waves,” Swain said.

Hawaii has already dealt with two near misses from tropical storms — Fausto to the north in July, and Moke to the south this past weekend — and one significant impact from Hurricane Lala. The islands aren’t out of the woods yet.

The hurricane center predicts a greater than 70% chance of a tropical storm or hurricane southeast of Hawaii next week. It is too early to say if the islands will be impacted, but the overall pattern is “putting Hawaii at continued risk for impacts from tropical cyclones moving through or originating in the central Pacific,” the agency said.

Central Pacific hurricane activity usually peaks in August, though strong El Niño years make the “occurrence of late season storms” in September and October more likely, according to the hurricane center. Warmer-than-normal waters south of Hawaii remain supportive of any tropical storms that move near the islands.