Marine Weather and Tide Forecast for Koloa, HI

SHORT TERM UPDATE
Issued at 800 PM HST Thu Apr 16 2026

Forecast remains on track for another mostly dry day across the state for Friday with a few exceptions. A weak upper level short- wave trough moving through the area on Friday will bring an increase of cloud cover and will provide some instability for some isolated thunderstorms over the slopes of the Big Island (moderate confidence) and possibly over Kauai (low confidence), if Kauai is able to get enough day time heating. Otherwise, we should see mostly dry conditions on Friday with an increase of mid to upper level clouds. Trade winds will also be filling in a bit more and could become moderate to locally breezy by Friday afternoon.



DISCUSSION
Issued at 403 PM HST Thu Apr 16 2026

Surface observations and a late morning advanced scatterometer pass revealed light to moderate easterly winds returning to the region today. Latest surface analysis shows that a trough is currently located about 130 miles north of Kauai, associated with a low pressure system that is now over 1600 miles northeast of the state. Though trades are gradually returning, they remained light enough today to support afternoon sea breezes, along with increased clouds and showers over select island interiors. In addition, afternoon satellite and radar imagery shows that mid- and high clouds associated with the subtropical jet continue to stream over the eastern half of the state. A few lightning strikes were detected on GOES GLM (Geostationary Lightning Mapper)
imagery this afternoon, but rainfall has been sparse and light statewide today.

High pressure building far to the northwest will quickly slide eastward over the next couple of days. This will mark a short- lived return to moderate easterly trade winds from tonight into the weekend. These moderate trades will likely be strong enough to limit sea breeze development to terrain sheltered areas of the islands. However, a disturbance aloft is expected to develop northwest of the state, and Kauai (along with its coastal waters) may be close enough in proximity to this feature to see increased showers and some isolated thunderstorm chances on Friday. In addition, daytime heating could also spark afternoon convection along the Big Island slopes. With this afternoon's forecast updates, isolated thunderstorms have been added for these two areas on Friday, with the central islands remaining drier.

By Saturday, winds will start to veer a bit more east-southeast as a low develops to our northwest, and eventually more southeast to southerly by Sunday. This southerly flow will draw moisture northward in the vicinity. As previous discussions have mentioned, as of now the low appears to track far enough north to limit heavy rain potential over the islands, though increasing instability and shower chances are possible during the second half of the weekend and into the first of next week. While moisture availability appears to be a limiting factor at this time, upper troughing (and an eventual upper low) developing over the state, at least some modest vertical motion, and cooling temperatures aloft warrant keeping an eye on the forecast from this weekend into early next week.

AVIATION
Issued at 800 PM HST Thu Apr 16 2026

Light to moderate easterly trade winds are gradually settling in tonight and will maintain steady through tomorrow. An upper level disturbance may provide additional showers to Kauai tomorrow afternoon with isolated thunderstorms possible. Otherwise, expect passing showers over windward and mountain areas, as well as afternoon showers over kona slopes remain. MVFR conditions may occur within showers and VFR elsewhere.

No AIRMETs are in effect.

MARINE
Issued at 800 PM HST Thu Apr 16 2026

Trough to the NW maintains gentle to moderate easterly trades through today. The strongest breezes will occur through the typical windy channels surrounding Maui and the Big Island.
Building high pressure then supports moderate to locally fresh easterly trades across the waters Friday into Saturday. Winds may briefly reach the Small Craft Advisory threshold late Friday through Saturday. Low pressure to our NW on Sunday will cause trades to weaken slightly and veer to ESE. Gentle to moderate ESE winds are expected Sunday into early next week.

Small background energy from the W will be possible this weekend into next week from Typhoon Sinlaku, but confidence remains low. A moderate NW to WNW swell is possible towards the second half of next week as Typhoon Sinlaku transitions to extratropical early next week. Low pressure advancing S along the W coast of the US next week should produce a moderate, medium period NE swell toward the islands by midweek.

A small to moderate, medium-period, SSE swell boosts surf along S shores through Friday then lowers over the weekend. Surf is expected to return to background levels along south facing shores by early next week. Surf along E shores remains below the seasonal average as trades remain light. However, increasing trades by week's end should bring a slight bump to surf over the weekend.

HFO WATCHES/WARNINGS/ADVISORIES
None.