Surface high pressure northwest of the Hawaiian Islands will slowly slide east over the next several days. Passing showers are possible over windward and mauka areas during this time period, mainly during the overnight to early morning hours. The next best chance for statewide rainfall should arrive Tuesday and Wednesday as increased low level moisture arrives with an old cold front drifting into the region.
Radar shows scattered trade showers moving west extending mainly from Molokai to Kauai county. Numerous showers are making it past windward areas and into leeward areas. This is expected to continue into the evening and overnight before decreasing Sunday. Winds have weakened slightly this afternoon, now averaging 5 to 15 mph with the windy areas gusting 20 to 30 mph.
An upper level ridge will remain centered on the state through Tuesday afternoon. After that, a weak upper level trough will move in from the west and stay close to the islands into next weekend. At the surface, a large high centered near 38N 165W will move east through Monday. A new high will temporarily take it's place Tuesday, before replaced yet again by a third high late next week. Bottom line is that there will be high pressure to the north, and trades will stay with us through the next seven days.
A decaying old front (now "just" a trough) will move through Monday afternoon through Monday night, bringing an increase in showers. Moisture from this feature is forecast to stall near the Big Island into Tuesday. There may be another brief increase in moisture from a similar feature late next week, but models are not good at timing these types of things that far in advance. Therefore, apart from the aforementioned increase Monday into Monday night, expect typical trade showers, mainly impacting windward and mauka areas, through the coming week. Wind speeds will be fairly normal for this time of year.
Breezy trade winds will continue into Sunday with brief periods of showers over windward and mountain areas, spilling into leeward areas at times.
AIRMET Sierra is in effect for mountain obscurations over north and east sections of Kauai, Oahu, Molokai, and Maui. Low clouds and scattered windward showers will maintain obscured terrain in this area.
AIRMET Tango remains in effect for low level moderate turbulence over and downwind of island mountains.
Fresh to locally strong trade winds will increase tonight as a strong 1034 mb high builds far north of the islands. The Small Craft Advisory (SCA) has been expanded to all waters to account for the strengthening trades. Winds will diminish gradually late Sunday and Monday as the high moves to the northeast, but a new north swell will push combined seas above 10 feet for exposed waters, likely prompting an extension of the SCA for most zones. Expect moderate to locally strong trade winds to require a SCA for the typically windy waters Tuesday through the remainder of the week.
A small north-northwest swell will hold through tonight, followed by a moderate, long-period north swell building on Sunday. The north swell (350 to 010 degrees) will produce surf near High Surf Advisory thresholds along north-facing shores, as well as some exposed eastern shores, on Sunday afternoon into Monday morning, and a Marine Weather Statement has been issued to highlight surges in north-facing harbors, mainly at Kahului and Hilo Harbors. The north swell will gradually decline late Monday through Wednesday. A tiny pulse of northwest swell will be possible late next week, followed a moderate swell next weekend.
Rough surf along east-facing shores will remain above seasonal average over the next couple of days due to elevated trade wind swell and some wrapping north swell. East shore surf is expected to be around seasonal average Tuesday through the rest of the week. Mainly small background level surf will persist along south- facing shores through much of the week, though a small long-period swell will be possible on Friday.
Small Craft Advisory until 6 PM HST Sunday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Big Island Windward Waters-Kaiwi Channel-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters- Maalaea Bay-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-Pailolo Channel.
