Hurricane Iselle was downgraded to a tropical storm just before 11 p.m. HST (5 a.m. EDT), however, its impacts will essentially remain similar. (LIVE BLOG: Hurricane Iselle Latest Updates)
The first hurricane warning for the main Hawaiian Islands since Hurricane Fernanda in 1993 was issued earlier in the week. Despite not making landfall as a hurricane, there is only one tropical storm on record to come in from the east and hit the Big Island, in 1958. Overall, Iselle is a rare -- if not historical -- tropical cyclone.
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.
Tropical storm warnings continue for Maui County, which includes the islands of Maui, Lanai, Kahoolawe and Molokai, the island of Oahu, which includes Honolulu, and Kauai County, which includes the islands of Kauai and Niihau.
A tropical storm or hurricane warning means those conditions are expected in the area. Warnings are typically issued 36 hours in advance of the onset of tropical storm-force winds. When a warning is issued, you should complete all storm preparations and, if directed by local officials, evacuate the area immediately.
As of 2 a.m. PDT (11 p.m. Hawaiian Standard Time) Friday, Iselle's maximum sustained winds are 70 mph.
Iselle is roughly 55 miles southeast of Hilo, Hawaii. The storm is moving quickly, between 15 and 20 mph, and steering currents are expected to continue to take Iselle on a west-northwest track over the next few days.
Iselle's center is forecast to continue sliding toward the west-northwest across the Big Island overnight Thursday night (local time), then track to the south of the rest of the island chain into Friday and Friday night.
Keep in mind a tropical cyclone 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). Forecast Wind Impacts
- Big Island: Winds of 60-70 mph with higher gusts, particularly over mountainous terrain, are expected into early Friday. Expect downed trees, power outages, and some structural damage.
- Maui County, Oahu: Winds over 40 mph, with gusts of 55-65 mph, particularly over mountainous terrain. Some downed trees, power outages, and minor structural damage is possible.
- Kauai, Niihau: Tropical storm-force winds (40+ mph) should begin Friday afternoon. Closest approach of center expected Friday evening. Some downed trees, power outages, minor structural damage possible. 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.
Here are specific impacts expected in Hawaii as Iselle moves in:
- Big Island: Surf heights will reach 15-25 feet Thursday and Thursday night. Coastal flooding, damage to property is expected along low-lying areas. High tide at Hilo Bay is 2:03 p.m. Friday. Up to 1-2 feet of flooding above ground level is possible with the arrival of the center of Iselle Thursday night into Friday.
- Maui County, Oahu: Surf heights from 10-18 feet through Friday. High surf combined with early afternoon high tide Friday afternoon may lead to some coastal flooding in low-lying areas.
- Kauai, Niihau: Surf will increase to 10-15 feet through Friday. High surf combined with early Friday afternoon's high tide may lead to some coastal flooding in low-lying areas.
After Iselle, Hawaii could eventually feel the effects of Julio this weekend. 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 reintensified 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.
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 ON WEATHER.COM: Hurricane Iselle in Pictures
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