textproduct: Honolulu

UPDATE

An update to clarify that the Flood Watch has been cancelled for Oahu but the Flood Watch will remain in effect for Niihau and Kauai through 6 AM HST tomorrow (Tuesday) morning.

SYNOPSIS

A surface trough is oriented NE-SW across Kauai County this afternoon, with thunderstorms forming and moving toward Niihau and Kauai as of 2 PM HST. This trough will move west tonight and remain to the west Tuesday. A new cold front will approach from the northwest Tue night into Wed, adding its moisture and convergence to the remains of the initial trough and moving back southeast toward Kauai County. The main area of concern for potential heavy rain for mid to late-week is therefore Kauai and Niihau. There is a chance that this feature could get near Oahu. After trending away from Oahu the past couple of days, the very latest guidance is moving back toward a higher chance of it reaching the island.

PREV DISCUSSION

/ISSUED 306 PM HST Mon Dec 15 2025/

Showers and thunderstorms were located in the Kauai Channel and over and near Kauai and Niihau this afternoon. These were moving northeast, and have a good chance to impact the island through the remainder of the afternoon and possibly in the early evening. Satellite images show lots of high clouds streaming northeast across the entire state, and this is expected to continue into tonight.

Models still show the surface trough near Kauai/Niihau this afternoon (the remains of an old cold front) moving north and west away from the state tonight and remaining there Tuesday. A new cold front will move in from the northwest Tuesday night, pushing an enhanced area of moisture and convergence toward Kauai County. Yesterday this time, models were trending weaker with this system, showing it not making it much farther east than Kauai. However, the latest models now indicate that it could make it to Oahu, or at least close enough to increase rain chances there. Moderate to heavy rain in Kauai County is likely Wed-Thu, and is now looking more possible over/near Oahu during the same time frame.

The area of moisture resulting from this next front appears to get hung up along an east-west axis near or just north of the state by Saturday. A surface high pressure system to our northeast is then forecast to send a round northeast to east trades into the state this coming weekend, and this will keep the area of moisture lingering over the state right into early next week. There is lots of uncertainty concerning how much rain there will be this weekend, but there appears to be a relatively high chance of clouds and a moderate chance at continued showery conditions.

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AVIATION... A surface trough near Kauai will lift north while ridging building in from the southeast will slightly strengthen southerly winds across the state through Tuesday. Numerous showers with pockets of heavy rain and isolated thunderstorms possible across the western end of the state tonight with the threat diminishing Tuesday. Light icing will be possible in layered clouds (140-FL240) over Kauai and Oahu tonight.

AIRMET Sierra posted for tempo IFR conditions across the entirety of Kauai, while AIRMET Sierra for tempo mountain obscurations for Oahu, Molokai and Lanai continue tonight.

AIRMET Tango for tempo moderate turbulence aloft FL240 to FL340 above Kauai and Oahu associated with the jet stream.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch until 6 AM HST Tuesday for Niihau-Kauai-

High Surf Advisory until 6 AM HST Tuesday for Niihau-Oahu North Shore-Maui Windward West-Kona-Kohala-Kauai North-Molokai Windward-Molokai North-Maui Central Valley North-Windward Haleakala-Big Island East-Big Island North.

Small Craft Advisory until 6 AM HST Tuesday for Kaiwi Channel- Maui County Windward Waters-Alenuihaha Channel-Big Island Windward Waters.