Marine Weather and Tide Forecast for Kahului, HI

DISCUSSION
A 1035 mb surface high is centered far north of Hawaii, but is driving breezy trade winds across the islands this afternoon.
Water vapor imagery shows an upper low just north of Kauai slowly moving southeastward. Radar and visible satellite show widely scattered low clouds and showers moving in from the east carried by the trade winds, with the upper level feature providing a little bit of enhancement to the showers. 00Z soundings show a strong, but slightly elevated inversion and precipitable water around 1.3 inches. Lihue mixed layer CAPE is sufficiently strong 1100 J/kg with 700-500 mb lapse rates 7.6 C/km. Most of the instability is focused above the trade wind inversion, which has been the limiting factor for thunderstorms today. Will continue to carry isolated thunderstorm coverage around Kauai and Oahu tonight and Friday, and the Big Island interior Friday afternoon due to the sea breeze/instability combination.

The upper low will remain in the vicinity of Kauai and Oahu tonight, then begin to lift northeastward on Friday allowing warming and stabilizing aloft by Friday night. Other than the thunderstorm chances, a wetter than normal trade wind pattern should prevail during the next couple days, favoring windward and mauka areas, along with more leeward spread to the shower activity.

The surface high will maintain the breezy winds through the weekend before weakening and sliding and closer to the state Memorial Day through the middle of next week, resulting in an easing of the trade wind flow back to moderate speeds. The airmass will further stabilize and dry out over the state this weekend, leading to a decrease in trade showers with drier conditions persisting into the middle of next week.

AVIATION
Moderate to locally breezy trade winds will persist into the weekend. Showers will focus over typical windward and mountain areas with a slight increase expected tomorrow morning as enhanced moisture moves through. Currently an upper level low is expected to provide enough instability to allow some of the showers to become heavy. Isolated thunderstorms are possible through tomorrow morning. These conditions could cause some locations to dip into MVFR range due to low visibilities and ceilings, but VFR should prevail for most of the period outside of any showers.

Isolated areas of upper level turbulence is possible over western island areas where the upper level low resides. An airmet for these conditions is possible for a brief time tonight.

AIRMET Sierra remains in effect for mountain obscuration over windward portions of Kauai. Improving conditions have been noted on FAA webcams and satellite on Oahu, Molokai, and Maui where the AIRMETs have been cancelled. Additional mountain obscuration is possible tonight as cloud bases lower below some of the higher elevation peaks with the diurnal cycle.



MARINE
High pressure to the distant NNW will maintain moderate to locally strong trade winds through the weekend, then weaken early next week to bring moderate to fresh trades to the area. An upper level low will linger over the state through tomorrow, enhancing trade wind showers and bringing the potential for isolated thunderstorms, mainly over Kauai and Oahu waters. A Small Craft Advisory for the windier waters and channels around Maui County and the Big Island remains in effect through Friday.

Surf along south facing shores will gradually build tomorrow through Saturday as a long period south-southwest swell is expected to fill in, producing near seasonal average surf through the weekend before declining early next week. Another long-period south-southwest swell is expected to arrive Wednesday into Thursday, bringing more near seasonal average surf to south facing shores.

East shore surf will remain near seasonal average through the weekend as trade winds persist, then gradually decline into midweek as the trades weaken slightly.

Tiny surf will prevail along north facing shores through early next week. A small to moderate medium period northwest swell will arrive late Wednesday into Thursday of next week, bringing above seasonal average surf.

HFO WATCHES/WARNINGS/ADVISORIES
Small Craft Advisory until 6 AM HST Friday for Kaiwi Channel- Maui County Windward Waters.

Small Craft Advisory until 6 PM HST Friday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.