Tropical Storm Iselle Update: Only Second Landfall On Record in Big Island of Hawaii; High Winds, Flooding Rain Continue (FORECAST)

August 8, 2014

Tropical Storm Iselle in a Friday morning update from the Central Pacific Hurricane Center, became only the second tropical storm on record to landfall on the Big Island of Hawaii early Friday morning. As of Friday evening, though, Iselle is west of the Hawaiian Islands and is exhibiting a weakening trend.

Iselle made landfall at 2:30 a.m. HST on Friday, Aug. 8 about five miles east of Pahala, with maximum sustained winds of 60 mph. The only other tropical storm on record dating to 1950 to come in from the east and hit the Big Island was in 1958, with peak sustained winds of 50 mph. Overall, Iselle is a rare -- if not historical -- tropical cyclone.

(LIVE BLOG: Tropical Storm Iselle Latest Updates)

There have already been reports of structural damage, trees downed, power outages, and some flooding. Roofs were reportedly removed from homes just southeast of Hilo late Thursday night. As of Friday morning, parts of the Big Island had already picked up over eleven inches of rain.

(MORE: Latest Iselle News)

Some outer rainbands have also affected parts of Maui County. Twelve-inch diameter tree branches were broken and Piiholo Road was closed by downed trees and powerlines in Makawao. Streets were flooded by 3-4 inches of water, there, as well. Winds have gusted as high as 60 mph on the island of Kaho'Olawe.

Iselle will continue a west-northwest track south of the rest of the island chain through early Saturday local time. It is possible Iselle may weaken to a tropical depression before becoming a remnant low later Saturday.

Keep in mind a tropical storm is not a point, but has impacts far from the center. Despite the center sliding south of Maui, Oahu and Kauai, Iselle will still bring bands of heavy rain, flash flooding, high surf and strong wind gusts to parts of Hawaii. Below is a breakdown of forecast impacts (all times in Hawaii standard time).

(FORECASTS/CONDITIONS: Hilo | Maui | Honolulu)

Rainfall, Flood Threat

A flash flood watch is in effect for all the Hawaiian Islands as heavy rainfall is likely, with rainfall totals locally up to 12 inches possible in some locations.

(ALERTS: Hawaii NWS flood watches, warnings)

The heaviest rain is most likely over the slopes of the Big Island and also the island of Maui. However, flash flooding and mud/rockslides are a threat through the entire island chain from the Big Island to Kauai.

Waves/Storm Surge

The Weather Channel's storm surge expert, Michael Lowry, points out that due to the lack of a continental shelf, coastal flooding in Hawaii has a different character than along the East Coast and Gulf Coast. Instead of being dominated by storm surge from wind pushing water onshore, Hawaii's coastal flooding concerns have far more to do with wave runup -- water literally running up the shore after waves crash onto the coastline.

After Iselle, Hawaii could eventually feel the effects of Julio this weekend.

(MORE: Double Trouble | Hawaii Hurricane History)

Iselle's History

Iselle bypassed tropical depression status and formed as a tropical storm in the eastern Pacific Ocean about 1075 miles southwest of the tip of Baja California on Thursday, July 31.

(MORE: Why Hurricanes Have Names)

Iselle gained strength as it moved west-northwest through open waters and became a hurricane on August 1. This made Iselle the fourth hurricane of the 2014 eastern Pacific hurricane season. On Saturday, August 2, Iselle's maximum sustained wind speeds increased to 110 mph, making it a Category 2 hurricane.

Iselle became a major hurricane on Sunday morning, August 3 when its maximum sustained winds reached an estimated 115 mph. It fell back to Category 2 status early Sunday evening, but then quickly re-intensified to Category 3 status late Sunday night with estimated winds to 125 mph. Monday afternoon, August 4, Iselle peaked as a category 4 hurricane with estimated maximum winds of 140 mph.

Iselle began weakening thereafter, and crossed the 140-degree West longitude line on Tuesday, August 5. This took Iselle from the Eastern Pacific basin into the Central Pacific basin. Per established convention, the storm retains its original name even while crossing into another basin with its own list of tropical cyclone names.

Iselle made landfall at 2:30 a.m. HST on August 8, about five miles east of Pahala, with maximum sustained winds of 60 mph. The only other tropical storm on record dating to 1950 to come in from the east and hit the Big Island was in 1958, with peak sustained winds of 50 mph. Overall, Iselle is a rare -- if not historical -- tropical cyclone.

By maximum wind speed, Iselle is the third-strongest tropical cyclone of 2014 in the Eastern Pacific basin, behind Amanda and Cristina. However, Iselle has now surpassed both of those to attain the highest accumulated cyclone energy (ACE) index so far this season. The ACE index combines maximum wind speeds with the duration of the storm to estimate the total wind energy generated during a cyclone's lifetime.

MORE: Hurricane Iselle in Pictures

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