Marine Weather and Tide Forecast for Lanai City, HI

DISCUSSION

Nil instability, weak forcing, and rather high mid-level static stability have allowed Oahu to dodge a potentially impactful flooding event. Little change is expected during the next several hours, so rain rates are expected to remain in check. Cancelling the Flood Watch for Big Island. Will draw back the ending time for Kauai through Maui to 6am tomorrow morning. Elected to retain portions of the Flood Watch to account for the onset of the favorable diurnal cooling period and ongoing convection in Maui County within the surface trough axis. As forcing weakens, so too will rain rates. Light showers and mid-level clouds are likely to linger over the western end of the state for the balance of the week before another shortwave pivots through and brings a slight uptick in rainfall on Friday or Friday night. This wave is modeled to be progressive and and likely not impactful.

Despite the grungy pattern that may hang over Kauai and Oahu through the week, for the first time in awhile, there is no potential event on the horizon. The large scale pattern is gradually migrating away from aggregate low pressure anchoring north of the islands, though high pressure struggles to build as the mid-latitudes transition toward a more progressive pattern. Light winds favoring onshore sea breezes each afternoon may trigger rather productive convection in terms of showers as the moisture-rich airmass lingers. Likewise, dewpoints will hover around 70 degrees until the dregs of this airmass are ushered westward by returning trades. Trades do return by late this week, but remain quite light and may not make much of a dent in local humidity.

AVIATION

Showers continue to move in over the islands this afternoon.
Kauai and Oahu are still expected to bear the brunt of this system's impact, however radar shows showers popping up over Maui County as well. Shower activity is still expected to simmer down this evening, however MVFR or worse conditions may still arise across several sites due to lingering moisture and low clouds.
Winds will remain light at less than 10 kts, with land-sea breeze direction at most sites.

AIRMET Sierra remains in effect for mountain obscuration above 1500 ft for Kauai, Oahu, Molokai, and Maui, as well as for IFR conditions at Lanai. These conditions are expected to remain today with the ongoing shower threat, with some relief expected later this evening as conditions dry out, however low clouds may remain due to light winds and lingering moisture.

AIRMET Tango is also in effect for 120-FL280, as this system is expected to create moderate turbulence as it passes over the islands. Conditions are expected to improve overnight heading into Monday.

Widespread cloud cover over the state today may also lead to moderate icing.

MARINE

A weak surface trough will linger in the vicinity of the central and northwestern islands into early next week, keeping moderate to fresh southeasterly winds to its east, and light to moderate southerly winds to its west. This weak surface boundary along with an upper level disturbance moving over the region is currently bringing another round of showers and the potential for isolated thunderstorms this afternoon into Monday. As the surface trough lifts northwest and high pressure to the northeast begins to take over at the surface, gentle to moderate easterly trades will gradually develop across the Hawaiian coastal waters by the end of the week.

A moderate, medium-period north-northwest swell (340 degrees)
generated by the formerly-gale force low north-northwest of the main Hawaiian islands is filling in along north and west facing shores this afternoon. This swell will maintain small to moderate surf through Monday, followed by a decline in northwest swell energy for the rest of the week.

A medium-period south swell will continue to decline through Monday.
By Tuesday, however, a new south swell will arrive, once again providing a boost to surf along south facing shores through mid week before gradually subsiding into the weekend.

Surf along east facing shores will remain below seasonal average with lighter than average trade winds near and upstream of the islands forecast through next week.

HFO WATCHES/WARNINGS/ADVISORIES
Flood Watch through tonight for Niihau, Kauai, Oahu, Molokai, Lanai, Maui, and Kahoolawe.