More tropical storms may follow Hilda near Hawaii

HONOLULU, Hawaii – While the impact from Hilda on Hawaii will be minimal, a strengthening El Niño will continue the potential for tropical systems tracking near Hawaii well into the fall.

Hilda, which is now very disorganized, will continue to weaken as it drifts westward.

Even though Hilda is weakening and the center will pass well south of Hawaii, some rain, squalls and rough surf will affect the islands through the weekend. Bathers, boarders and boaters should heed all advisories until they are lifted.

Most of the impact from Hilda will be felt on the Big Island of Hawaii. Combined with prior rainfall from Guillermo, enough rain will fall along the east-facing slopes to cause flash flooding and mudslides.

Rainfall will average 1-2 inches on the Big Island with 4-8 inches drenching the eastern slopes of the mountains. A couple of remote locations can receive close to a foot of rain.

According to AccuWeather Meteorologist Andrew Mussoline, “A few showers will spread westward to some of the other islands.”

Flooding problems in all but the Big Island will be very isolated.

“For all practical purposes, this is a Big Island storm in terms of rain and locally gusty winds,” Mussoline said.

Portions of the islands are in need of rain. For example, Honolulu has received less than 50 percent of its normal rainfall since Jan. 1. Hilda could assist in alleviating some of the dryness, but drought-busting rainfall is not likely.

During El Niño years, the number of tropical systems developing in or moving into the Central Pacific basin is higher than average and can result in a significant impact on Hawaii.

El Niño is attributed to warmer-than-average waters of the tropical Pacific Ocean. When waters are warm, there is potential for stronger and greater numbers of tropical systems.

On average, four to five tropical systems affect the Central Pacific basin each year and most originate from the Eastern Pacific. So far, there have been five named systems in the Central Pacific during 2015.

Strong winds aloft typically cause the westward-moving systems to weaken. So far this season, Hilda and Guillermo have fallen into that mold. Even Iselle (2014), the strongest system to hit Hawaii from the East, weakened considerably before hitting the Big Island as a tropical storm.

With El Niño forecast to remain strong into the fall, the risk of a tropical system impacting the nearby waters of Hawaii will continue through September and into October. However, steering winds tend to shift during the fall.

According to AccuWeather Meteorologist Anthony Sagliani, “By late October, winds aloft usually become too hostile for tropical systems to form or maintain themselves over the Central Pacific.”

Hurricane Iniki, the strongest tropical system to ever strike Hawaii, occurred in September and moved up from the South. Iniki occurred at the end of the 1991-1992 El Niño.

“Iniki was probably a once in 100-year storm, due to its strength and where it came from,” Sagliani said.

Iniki struck Kaua’i as a Category 4 hurricane with sustained winds of 145 mph.
Storms have formed later in the fall and have tracked up from the Southwest toward Hawaii during El Niño.

Hurricane Iwa formed in late November of 1982, and it tracked from Southwest to Northeast, farther West than Iniki. A significant El Niño occurred during 1982-1983.

Hurricane Nina occurred during the El Niño of 1957-58 during late November into December.

However, people should not let their guard down for the balance of this season even though climatology favors tropical systems to weaken coming in from the east and systems from the south being very rare. There is always the risk of a system that does not fit the mold.

There is a chance of more systems moving in from the East and it is possible one of those may maintain strength to cause significant problems for the islands. There is also the risk of a system swinging up from the south as El Niño continues and steering winds begin to shift around this fall.