Hurricanes Iselle and Julio continue to churn towards Hawaii at this hour, and most of the state's major cities are preparing for a period of dangerous weather conditions tomorrow and Friday. Here's what to expect as both storms threaten and impact the country's 50th state.

5:00PM Update: Hurricane Hunters are finding winds of 100-105 MPH at the surface in Iselle. This means that Iselle is strengthening as opposed to weakening. In response, the CPHC has upgraded the Big Island to a hurricane warning.

The Basic Setup

We have two hurricanes running back-to-back towards the Hawaiian Islands right now. Hurricane Iselle is the closest, and it's starting to feel the effects of a huge slug of dry air that's tearing the storm apart. The above water vapor imagery shows Iselle struggling against the dry air (yellow and orange colors). Behind Iselle we've got Julio, a newly-minted hurricane that is going to follow a similar but more northerly track than Iselle.

The biggest threat to Hawaii right now comes from Iselle.

Where is Iselle going?

Iselle looks to be on a direct path to make landfall on the Big Island on Thursday night, with the center of the storm passing to the south of the rest of the Hawaiian islands during the day on Friday and Saturday.

The islands are still in the cone of uncertainty, and tropical storm force winds currently extend 140 miles away from Iselle's center. The new forecast as of 11AM HST brings upgrades Maui, Kahoolawe, Lanai, and Molokai to tropical storm warnings, and the Big Island is now under a hurricane warning.

How strong will it be when it hits?

The latest advisory from the Central Pacific Hurricane Center shows Iselle packing sustained winds between 75 and 80 MPH by the time it makes landfall, with higher gusts possible. Provided that the center stays close to the forecast path and makes landfall on the Big Island, the eastern side of the island will take the brunt of Iselle's energy.

Again, if the center tracks south, the storm will have less of an impact, and it if tracks further north, the strongest winds could impact more heavily populated islands.

What are the greatest impacts?

Aside from the potential for 75+ MPH winds, Iselle's impacts will also include heavy rainfall, high surf, and rip currents. The heaviest rain is likely to fall over the Big Island if the current forecast track holds, but the entire state of Hawaii is under a flash flood watch in anticipation of very heavy rainfall. As always, mountainous terrain will enhance any precipitation that falls, creating extremely heavy rain that will bring with it the threat for flash flooding and mud/landslides.

For reference, the latest National Weather Service forecast for Hilo shows maximum wind gusts reaching 87 MPH along with about 5 inches of rain.

What about Julio?

Behind Hurricane Iselle we've got Hurricane Julio, which is following a similar track to Iselle but further to the north. The latest forecast from the National Hurricane Center brings Julio north of the Hawaiian Islands, but keeps them within the cone of uncertainty. It warrants close attention towards this weekend just in case the storm shifts to the south of its current forecast track.

Hawaii is usually lucky when it comes to escaping intense tropical cyclones; Iselle will be the strongest tropical system to hit the state since Hurricane Iniki back in 1992.

[Satellite image via GOES / maps by the author]