At a Glance

The Eastern Pacific hurricane season officially begins May 15.Hurricanes and tropical storms in this basin can affect the southwestern U.S. and Hawaii.The last few years have shown how Eastern Pacific storms can be a threat to the U.S.

The Eastern Pacific hurricane season officially begins this Sunday, and while it's often overshadowed by the Atlantic Basin, it can sometimes bring significant impacts to parts of the United States.

The Eastern Pacific season's start date of May 15 is just over two weeks earlier than the official beginning of the Atlantic season. This is due to warmer waters and the fact that wind shear is typically weaker earlier in the season compared to the Atlantic.

Agatha will be the name given to the first tropical storm that forms in the Eastern Pacific this year.

2022 Eastern Pacific Hurricane Season Names

Many Eastern Pacific tropical storms and hurricanes move away from land and are only a concern to shipping interests. But sometimes, the weather pattern can allow these systems to affect Mexico, Central America and the southwestern U.S.

Hawaii is also occasionally threatened by tropical storms and hurricanes that make the long trek from the Eastern Pacific into the Central Pacific.

Here's a breakdown of how Eastern Pacific storms can be a threat to the Southwest and Hawaii, including recent examples.

Southwest Tropical Flood Threat

Arizona is the Southwest state with the most tropical storm encounters. According to the National Weather Service in Tucson, have remained intact and impacted Arizona directly since 1965. Five of these were tropical storms with sustained winds of 39 mph or higher.

Moisture from the remnants of Eastern Pacific storms can sometimes be drawn northward into the Southwest.

Flooding rainfall is typically the biggest concern from any tropical systems that survive the journey into the southwestern U.S. Sometimes, this rainfall can be triggered by the remnant spin of former Eastern Pacific tropical storms and hurricanes.

While such a storm might no longer be intact, the remnant tropical moisture can fuel drenching rains as it moves into the region.

Last year, Hurricane Pamela made landfall in Mazatlan, Mexico, in mid-October and then fizzled shortly thereafter. However, its remnant moisture was pulled into a cold front over central Texas, where it brought a soaking of , according to the National Hurricane Center.

In August 2020, moisture from short-lived Tropical Storm Fausto played a role in a , including around the Bay Area. The lightning started several devastating wildfires in the region since the storms had little rainfall.

Moisture from both Tropical Storm Ivo and reached the Southwest in 2019. Moisture from Ivo's remnants triggered flash flooding in Las Vegas in late August.

The interaction between moisture from the remnants of in July 2015 and a disturbance moving into California resulted in historic July rains in Southern California. Both Los Angeles and San Diego broke all-time July rainfall records at a time of year when rainfall is almost always scant in Southern California.

Also in 2015, moisture partially associated with led to flooding that killed 20 people in Utah on Sept. 4, according to the .

From the Eastern Pacific to Hawaii

Hawaii was impacted by the remnants of former Eastern Pacific Hurricane Linda in August of last year. The hurricane's leftover moisture and area of low pressure .

was the last close call for the Hawaiian Islands in July 2020.

Unlike a number of other hurricanes that originated in the Eastern Pacific, Douglas didn't lose its intensity that quickly as it tracked into the Central Pacific toward Hawaii.

Hurricane warnings had to be issued for Maui, Oahu and Kauai since Douglas' forecast track was a potential threat to those islands.

Luckily, the southern eyewall of Douglas passed just north of Maui, Oahu and Kauai, sparing those islands from seeing the worst of the hurricane's strong winds and heavy rainfall.

In the case of Oahu, the hurricane's center passed just 30 miles north of the northern tip of Oahu on July 26.

Track of Hurricane Douglas in July 2020.

Hawaii approach in 2018 was another close shave for the nation's 50th state.

Lane developed over the Eastern Pacific in August 2018 and crossed into the Central Pacific Ocean.

After intensifying to a Category 5 hurricane southeast of Hawaii, Lane weakened significantly as it passed more than 100 miles south of the island chain. Parts of the islands were swamped by flooding rainfall.

Also in 2018, was the first tropical storm to make landfall over Lanai and Maui. Olivia triggered flooding on Maui and downed trees on Maui and Oahu a few weeks after Lane.

In 2014, Iselle made landfall on the Big Island of Hawaii as a tropical storm on Aug. 8. There were reports of structural damage, trees downed, power outages and some flooding on the Big Island.

Satellite image of Iniki at landfall.

(Central Pacific Hurricane Center)

Hurricane Iniki in 1992 might be the most serious example of the impacts Eastern Pacific tropical cyclones can generate in Hawaii. Iniki is the costliest hurricane in Hawaii's history; It originated in the Eastern Pacific on Sept. 5 and moved into the Central Pacific, where it became a powerful hurricane.

The island of Kauai was hit especially hard by damaging winds when Iniki made landfall there as a Category 4 storm. Many structures were wiped out by storm surge flooding and large, battering waves along the southern coast.

Hawaii is usually protected from tropical storms and hurricanes approaching directly from the east due to cooler waters and strong winds aloft, which contribute to weakening. Many other tropical storms and hurricanes have passed safely to the south of Hawaii because of high pressure north of the islands.

It's the rare cases illustrated by Iniki and Lane – when a hurricane first moves south of the island, then arcs northward – that pose a greater threat to the state.

A California Rarity

Map showing the position of the 1858 San Diego hurricane on Oct. 2.

(Michael Chenoweth and Christopher Landsea/NOAA)

Southern California is the only portion of the Pacific coastline in the Lower 48 that could see a tropical storm or hurricane landfall from the Eastern Pacific. Although such an event is extremely rare, history shows it can happen.

On Oct. 2, 1858, the slammed into San Diego. Sustained hurricane-force winds resulted in extensive property damage.

Only one tropical storm has made landfall in Southern California since then. In September 1939, a tropical storm with winds of 50 mph hit Long Beach. Flooding caused moderate crop and structural damage, according to the NWS in Oxnard. High winds surprised the shipping industry in the area, killing 45 people.

While technically not a tropical storm at the time, what had been Hurricane Kathleen raced northward into the desert of southeastern California in September 1976. Wind gusts to 76 mph were measured in Yuma, Arizona, and a 4- to 6-foot wall of water destroyed 70% of homes in Ocotillo, California.

Cool ocean temperatures in the path of the tropical systems trying to reach the Pacific coast are the primary reason landfalls are so rare in Southern California. Coastal waters get dramatically cooler as you move north along the coast from Mexico.

As in 1858, any hurricane would have to be moving fast enough, over waters just warm enough, to maintain its intensity on the way northward in order to have a California landfall.

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