Bands of low level clouds with embedded showers will focus mainly along windward and mauka areas as moderate trades hold into Monday. Winds will become light and veer southerly Tuesday as a front approaches the state from the northwest. The front is expected to move over the state during the second half of next bringing a wetter period.
Latest surface analysis shows a trough of low pressure roughly 250 miles west of Kauai early this morning where some isolated thunderstorms are being triggered just outside of the coastal waters. This trough is expected to weaken and lift north today, keeping the threat of thunderstorms west of the coastal waters. Overnight rainfall totals on Kauai range from 0.06 to 2.0 inches for the wetter regions of Kauai. Expect showers to trend down during the day as a drier airmass with limited upstream clouds and showers moves through. Moderate trades will ease slightly tonight as an upper level trough moves overhead. This slight instability overnight could help provide isolated moderate to locally heavy rainfall but should be brief and mainly focused along windward and mauka areas. The exception could be the Kona slopes of the Big Island as seabreezes strengthen this afternoon into the early evening hours.
The upper level trough will continue to dig southeast of the state through Sunday and eventually form a closed low east of the state Monday. This pattern should place the state in an area of subsidence as low to mid level ridging builds in from the west, creating a highly stable, moderate trade wind pattern. Some bands of low level clouds and showers trapped within the trade wind flow, enhanced by the upper low, will mainly focus along windward and mauka areas.
Extended guidance continues to show a cold front approaching the state from the northwest Tuesday allowing winds to become light to gentle and veer southeast. Details on the timing and exact impacts as the front moves through the state are still unknown. The EC model brings the front in Wednesday night with more modest impacts than the GFS which brings the front in around Thursday morning with stronger frontal lift and upper level dynamics resulting in a wetter pattern. Thus will continue to monitor and update the forecast with the latest details.
Moderate to locally breezy east-southeasterly winds will gradually weaken today as the surface high to the far northeast weakens and drifts further eastward. A slightly drier airmass has filtered in limiting shower activity over windward and mountain areas. Expect mainly VFR conditions through today. Brief MVFR conditions are possible with passing showers.
No AIRMETs are currently in effect or expected.
A surface trough west of Kauai will continue to weaken and drift slowly westward away from the islands through Sunday. A surface high pressure ridge will remain north of the Hawaii region, winds flowing around this ridge will produce moderate to locally strong easterly trade winds today, then wind speeds will slowly decrease from Sunday onward. Lighter southeast to south winds are forecast from Tuesday to Wednesday as another cold front moves into the region from the northwest. A consensus of weather model guidance suggests this cold front may move into the western Hawaiian islands from late Wednesday into Thursday.
A Small Craft Advisory (SCA) remains in effect for the typically windier waters around the islands in Maui and Hawaii Counties. Trade winds will drop below SCA thresholds by tonight.
The current medium period north-northwest (340-350 degree) swell continues to slowly decline this morning. Buoy observations from National Data Buoy Center stations 51001 and 51101 just northwest of Kauai show a gradual downward trend. The latest swell model guidance confirms this downward trend as the current north-northwest swell energy will gradually fade into Monday, bringing surf back down to below average levels for this time of year. The next two long to medium period overlapping northwest (310-320 degree) swell pulses will arrive on Monday and Tuesday, boosting surf along north and west facing shores possibly reaching marginal advisory levels by Wednesday.
Choppy east shore surf will remain small and decline this weekend as trades ease. Expect minimal background energy for south facing shores through the next few days, other than a slight bump this weekend.
Peak monthly tides combined with water levels that are running higher than predicted will likely lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible around the early morning peak tide through Sunday.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
