Marine Weather and Tide Forecast for Kaneohe Station, HI

DISCUSSION
The band of heavy showers along a prefrontal convergent boundary that moved across Kauai earlier this morning has now pushed east into the Kauai Channel, with current radar showing mainly light showers moving across Kauai from the southwest in its wake.
Automated rain gage reports show some locations across Kauai received over an inch of rain over the last 6 hours.

The line of moderate to heavy showers is holding together over the Kauai Channel as it continues to progress eastward, with isolated showers streaming up from the south and occasionally moving into leeward areas of Oahu and Maui County. As this prefrontal convergent boundary approaches Oahu late this afternoon or evening, general consensus from model guidance has it falling apart, decreasing the threat for localized flooding. Even though the boundary will become less defined, it will likely still bring showers, some potentially heavy with precipitable water values near 2 inches, to Oahu and perhaps portions of Maui County late this afternoon or evening before model guidance shows the axis of moisture retreating back to the northwest tomorrow morning.
Meanwhile, the weak cold front (currently still around 170 miles northwest of Kauai) will approach Kauai this evening and dissipate across the western end of the state. Both of these surface features will maintain rain chances across the western half of the state through tomorrow. Thunderstorm potential will remain low, but still present, mainly along the prefrontal convergent boundary where the best combination of moisture, lift and instability will be lined up.

By Wednesday, the surface ridge to the northeast of the state will take control and moderate ESE trade winds will return and persist through the rest of the week. As such, showers will once again focus over windward coasts and slopes, with some localized sea breeze activity bringing clouds and a few showers to leeward locations. Mid-level ridging will build over the state from the west during the latter part of the week, increasing stability and suppressing shower activity. Another shallow cold front will approach the islands from the northwest this weekend, weakening the surface ridge and producing lighter southeast winds across the region. With these lighter winds, land and sea breeze development may become more prevalent.

AVIATION
A NE-SW oriented band of broken to overcast low clouds over the Kauai Channel has embedded towering cumulus with tops near 25 kft, with potential for isolated thunderstorms with tops near 35 kft. This band is expected to move E toward Oahu through the day while gradually weakening, arriving over NW Oahu in the next couple of hours, and over SE Oahu later this afternoon. Widespread MVFR VIS/CIG in SHRA can be expected within the band, and AIRMET Sierra is in effect for mountain obscuration on Kauai and Oahu.
Improving conditions are expected over Kauai this afternoon.

This band will stall and gradually dissipate near Oahu/Molokai overnight. A surface high will move rapidly E to the N of the islands, supporting a light to moderate E trade wind flow that will likely push remnant moisture into windward slopes on Tuesday.

MARINE
A front over the northwest offshore waters will continue to move eastward today then stall and dissipate over the central waters tonight into Tuesday. Over the coastal waters, we have a band of moisture over the Kauai Channel this morning, which is moving into Oahu waters now. Although lightning has not been seen with this band of showers, there will be an outside chance for some lightning later today around Kauai and Oahu waters. Light winds out of the south across the western half of the state will shift towards the north this evening over Kauai behind the front.
Moderate east to east- southeast winds will return statewide on Tuesday afternoon and continue through the remainder of the week as a transient high pressure passes north of the area.

A series of west-northwest to northwest (300-320 degree) swells are expected this week with the first of the series arriving today. Long-period forerunners are already seen on the nearshore buoys this morning and surf is expected to steadily build throughout the day and peak tonight into Tuesday. A High Surf Advisory (HSA) is in effect for exposed north and west facing shores of Niihau, Kauai, and Oahu from noon today and will likely expand to parts of Maui County tonight and the west facing shores of the Big Island on Tuesday. In addition, A Small Craft Advisory (SCA) for hazardous seas will likely be needed tonight for waters exposed to these large swells. Another reinforcing swell is expected on Wednesday, which should maintain advisory level surf along north and west shores through the middle of the week and possibly into Thursday.

Due to the lack of strong trades, small surf is expected along east facing shores this week. A slight increase is possible Tuesday through the second half of the week due to the light to moderate east to east-southeast trades. Surf along south facing shores should see a small boost on Wednesday as a small south swell fills in and should produce some rideable surf throughout the second half of the week. Select exposures could also see some small wrap from the large west-northwest swells over the next several days.

HFO WATCHES/WARNINGS/ADVISORIES
High Surf Advisory until 6 PM HST Tuesday for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Kauai North.