textproduct: Honolulu

SYNOPSIS

An upper level trough will bring continued heavy rain to the state through the weekend. Flash flooding, thunderstorms, and high- elevation snow are all in the forecast. Winds may increase Saturday, but latest model trends are lowering confidence in this possibility. We expect to see trades return Monday night and last through the work week. Showers will continue windward and mauka even though overall conditions will dramatically improve. A new storm system is possible next weekend.

DISCUSSION

Issued at 342 PM HST Fri Mar 20 2026

This afternoon radar (as of 3:40 PM HST) shows a large area of moderate to heavy showers over Maui County, and scattered showers over Kauai and Oahu. Light showers are expected to move into northwest Big Island this evening. Winds were generally out of the south at speeds averaging 10 to 20 mph with gusts 20 to 30 mph. Flood warnings are still in effect on Oahu, with flood advisories on Maui County. Rainfall amounts on Oahu in the past 6 hours were generally in the 2 to 6 inch range, with a maximum of 8.58 inches at Wahiawa.

The forecast remains largely unchanged, with a flood watch in effect for all areas except the peaks on the Big Island through Sunday. Periods of showers, heavy at times, will continue to move through the islands. Southwest flow aloft will remain in place thanks to an upper level trough to our west. Smaller "pieces" of energy will move through this trough and occasionally boost the shower activity, possibly leading to isolated thunderstorms. The exact location of these increased showers is impossible to know ahead of time (beyond the state of modeling science out here in the middle of the ocean). Therefore, folks should be aware that flooding will continue to be possible in all areas where the flood watch has been issued.

Forecast models are reasonably consistent in keeping the axis of heaviest rainfall over the central islands tonight and Saturday, then shifting it slowly eastward Saturday night into Sunday. This will slowly take the risk of flooding eastward with it. Some drying will occur from Monday into Wednesday as trade winds become established over the state, but windward areas will see numerous light to moderate showers. Winds are expected to be a little weaker both Saturday and Sunday (in most areas) than they have been today. The exception will be the peaks on the Big Island, where winds will approach wind advisory criteria Saturday evening through Sunday morning. Several inches of snow are likely to fall on the summits Saturday night into early next week.

The long range forecast shows the possibility of another trough moving into the area from the northwest late next week. At this time, the setup is not a kona low system, but could push a cold front through the state. Details will become available as we get closer in time.

AVIATION

Issued at 342 PM HST Fri Mar 20 2026

Bands of rain with embedded heavy showers and storms have been moving through Oahu and Maui county today. These rainbands are producing periods of IFR to LIFR CIGS/VSBYS, which will persist into the weekend as an upper level trough approaches from the west. Kauai and Big Island are expected to be mostly VFR through tonight, with MVFR conditions possible within an occasional shower.

Low-level winds continue to be out of the S-SSW, and may veer more SW over the western half of the state on Saturday. Winds are strongest over Maui county, with gusts reported up to 39 kt at PHOG. These winds may result in localized mechanical turbulence leeward of terrain. Winds will remain gusty through the evening, but gradually weaken through the weekend.

AIRMET Sierra for mountain obscuration is in effect across all islands except Big Island, and will likely continue into the weekend. AIRMET Tango is in effect for moderate turbulence downwind of terrain for Oahu and Maui county below 090. AIRMET Zulu for light icing in the 140-FL260 layer will continue to be a concern within deeper cloud layers associated with the upper level disturbance.

MARINE

Issued at 342 PM HST Fri Mar 20 2026

Light to moderate S winds may strengthen tonight as surface low pressure west of Kauai deepens. Moderate to locally strong S/SW prevail through Saturday, and periods of heavy showers and thunderstorms are expected. The low will lift north on Sunday allowing moderate N winds to develop around Kauai which will then veer to NE and spread south. Fresh to strong NE winds may require a Small Craft Advisory over most waters.

N swell will increase into Saturday in maintenance of moderate swell through the weekend along N facing shores. A small, overlapping WNW swell then arrives late Saturday and holds through Monday. Surf along E shores remain well below average through the weekend. NE trades then develop early next bringing increase NE fresh swell and an increase in short period choppy surf which may approach the High Surf Advisory threshold.

A moderate S swell slowly diminishes through today followed by a small reinforcing SSW swell this weekend into Monday. Smaller surf is expected along south facing shores through the remainder of the week.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through Sunday afternoon for Big Island East-Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Central Oahu-East Honolulu-Ewa Plain-Haleakala Summit- Honolulu Metro-Kahoolawe-Kauai East-Kauai Mountains-Kauai North- Kauai South-Kauai Southwest-Kipahulu-Kohala-Kona-Koolau Leeward- Koolau Windward-Lanai Leeward-Lanai Mauka-Lanai South-Lanai Windward-Maui Central Valley North-Maui Central Valley South- Maui Leeward West-Maui Windward West-Molokai Leeward South- Molokai North-Molokai Southeast-Molokai West-Molokai Windward- Niihau-Oahu North Shore-Olomana-South Haleakala-South Maui/Upcountry-Waianae Coast-Waianae Mountains-Windward Haleakala.

Winter Storm Watch from Saturday evening through Sunday afternoon for Big Island Summits.