412 FXHW60 PHFO 162009 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1009 AM HST Wed Apr 16 2025 .SYNOPSIS... An approaching front from the northwest is pushing a ridge over the islands. This is resulting in light winds over the islands, leading to afternoon sea breezes and overnight land breezes. As a result, expect to see more clouds and some showers this afternoon. The approaching front will bring more clouds and showers to the region starting tonight, and the instability associated with the system will bring the possibility for heavier showers and thunderstorms through Friday. && .DISCUSSION... No changes to the forecast at the moment, but anticipate making some tweaks to various fields with the afternoon package to fine tune some aspects for the first 36 hours. Specifically will be looking at areas of heavy rain and adjustments to QPF. A weakening cold front northwest of Kauai is moving towards the islands, pushing a ridge over the islands. This in turn is bringing light winds to the region, resulting in afternoon sea breezes that will bring an increase in clouds and showers to the interior of the islands today. The front is expected to continue to weaken over the next 24 hours, while staying just northwest of Kauai. Surface winds are expected to remain light through Friday. Meanwhile, an upper level trough moving over the islands will bring colder than normal temperatures to 500 mb. Models, both globally and higher resolution, show good agreement with 500 mb temperatures getting to -13C. The models are also in good agreement with precipitable water values reaching 1.5 inches, which is above normal for April. This unstable airmass will likely produce some heavy showers and thunderstorms. These are not expected to be a line of storms that will be tracked down the island chain, but rather more pop-up storms. At this time, we are not expecting widespread flooding issues, so no Flood Watch is being issued. We can expect the possibility for some localized flooding in heavier showers. The upper level trough moves to the east Saturday, with a more trade wind pattern setting up at the surface for the weekend and early next week. Heading into the middle of next week, another wet pattern is being suggested by the global models. && .AVIATION... Wind speeds are on the decline as an approaching front stalls NW of the islands. Light and variable winds will develop over Kauai and Oahu while light to moderate ESE flow will likely persist over Maui and the Big Island. VFR conditions will prevail in the short term, and no AIRMETs are currently posted, but the island atmosphere will become increasingly unstable over the next 12-24 hours as a sharp trough aloft passes overhead. The trough will bring the potential for localized heavy showers/IFR VIS CIG and a slight chance of thunderstorms, as well as increased potential for moderate to severe turbulence aloft. && .MARINE... The slow approach of a cold front just entering our northwest offshore waters has weakened nearshore east-southeast winds. As this front stalls just west of the islands today, western water light and variable breezes around Kauai will become more localized daytime onshore and overnight offshore breezes. Elsewhere, gentle to moderate east southeast winds will persist over smaller island windward waters and around Big Island the next few days. As surface high pressure strengthens far northeast of the state, a brief return to fresh to locally strong easterly trades is possible this weekend. There will be an increased chance for widespread heavy showers and thunderstorms from tonight through Friday in response to the passage of an upper level trough over the state. Surf along exposed north and west-facing shores will continue to diminish today as the latest northwest swell fades away. An upward trend in surf is expected Thursday as a moderate size north northwest swell arrives and builds down the island chain. North and west shore surf may near advisory levels Thursday night into Friday during the peak of this swell. A downward trend is expected as the swell turns out of the north this weekend. East-facing shore chop will remain low into Saturday. A slight uptick in trades will result in a steady rise of eastern wind waves early next week. Surf along south-facing shores will remain small through the week with the passing of overlapping background south swells. A larger south southwest swell may arrive next Tuesday. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...M Ballard AVIATION...Birchard MARINE...Blood