Moderate trade winds with embedded showers favoring mainly windward and mauka areas are expected into Sunday, followed by drier conditions early in the work week. By Tuesday and Wednesday, winds will become light and veer southerly as a front approaches the state from the northwest. The front is expected to move over the state during the second half of the week bringing increased shower chances.
During the day today, the surface trough west of Kauai has continued to weaken and lift northwestward away from the main Hawaiian Islands. Meanwhile, drier conditions have been observed across the state today, with latest satellite and radar imagery showing very few clouds or showers. Also of note, episode 38 of the ongoing Kilauea eruption began this morning just before 1900 UTC, sending a plume composed primiarily of water vapor and sulfur dioxide gas (possibly with Pele's hair and ash) to near 35,000 feet. This plume then spread eastward over portions of the Puna District due to strong westerly flow aloft. However, as of 0130 UTC, radar echo tops and webcams show that emissions from Kilaua have reduced and lowered back down to about 20,000 feet, and are now being transported in the more typical southwesterly direction within northeasterly flow.
Moderate trades will continue to decrease slightly tonight as an upper level trough moves overhead. This slight instability overnight could help provide some enhanced showers, but these should be brief and mainly focused along windward and mauka areas. Model guidance is also suggesting that a band of moisture, currently seen on regional satellite imagery within the offshore waters to the east, will arrive during the morning hours on Sunday, sustaining windward shower chances for mainly the eastern end of the state.
The upper level trough is expected to continue digging southeast of the state Sunday and eventually form a closed low east of the state early Monday. As low and mid level ridging builds in from the west, stable and mostly dry conditions are expected with moderate trade winds. Any showers that do occur would be a result of brief pockets of low level moisture trapped within the trade wind flow, and would mainly focus along windward and mauka areas. The one exception is for the Kona slopes of the Big Island, where typical sea-breeze induced cloud buildups and a few showers will be possible during the day.
Models continue to indicate that a cold front will approach the main Hawaiian Islands from the northwest Tuesday. As this occurs, background surface winds will become light and veer southeasterly, allowing for daytime sea breezes and nighttime land breezes ahead of its arrival. Timing and impacts of the front remain uncertain, with the ECMWF offering an earlier arrival late Wednesday and more modest impacts than the GFS's later arrival on Thursday with stronger lift and upper level support for enhanced shower chances. Will continue to monitor and update the forecast with the latest details as they become more clear over the next couple of days.
Moderate east to east-southeast tradewinds will continue through tomorrow. A slightly drier airmass settled over the state will continue limiting shower activity through the evening and overnight hours. Brief MVFR conditions are possible with passing showers primarily over windward and mountain areas. VFR conditions will prevail.
Kilauea's eruption earlier this morning produced an ash cloud reaching FL350, but has continued to decrease in altitude throughout the afternoon. SIGMET series Sierra covers the ash cloud, and will likely be dropped tonight as impacts diminish.
No AIRMETs are currently in effect, but an AIRMET Tango for moderate turbulence between FL290-FL360 will likely be needed tonight as an upper level trough moves down the island chain starting from Kauai. This is expected to continue into tomorrow, affecting islands from Kauai through Maui.
A surface high pressure ridge will remain centered to the far northeast of the main Hawaiian Islands, producing moderate to locally fresh trade winds this evening that are expected to slowly decrease from Sunday onward. Lighter southeast to south winds are forecast from Tuesday into Wednesday as a 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.
The current medium period north-northwest (340-350 degree) swell continues to slowly decline this afternoon. Buoy observations and swell model guidance trends agree that this 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 and possibly reaching marginal advisory levels by Wednesday.
Choppy east shore surf will remain small and decline this weekend as trades gradually ease. Expect minimal background energy for south facing shores through the next few days, despite 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.
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