Stable conditions with light winds will persist through Sunday. A pair of cold fronts will impact the state during the upcoming week with the first cold front expected Sunday night through Monday night. Expect showers to increase along the frontal boundary with periods of moderate rain. Behind the front, expect breezy north winds and a cooler and dryer airmass. The second front looks to affect the islands Wednesday into Thursday.
A weak trough of low pressure continues to linger north of the state this morning and has allowed for some clouds and some isolated showers overnight. 12Z soundings from Lihue and Hilo continue to show above normal precipitable water values at around 1.5 inches with bulk of the moisture located in the lower levels. With the low level moisture in place today, we should see some scattered showers develop by mid day today due to the sea breezes. Most of the shower activity should be across interior and mountain areas and rainfall intensity should remain light to moderate due to an upper level ridge building across the state today. For Sunday, weather conditions will be somewhat similar with sea breezes developing once again, but generally shower activity will be less due to drier lower levels.
Starting Sunday evening, a cold front will begin to approach Kauai and we could see showers increasing ahead of the front with southerly winds also gradually strengthening. Models are in very good agreement on the timing with the front crossing Kauai and Oahu Monday morning, then continuing down the island chain through Maui County in the afternoon. A band of moderate showers will accompany the front, but the threat for flash flooding appears low. By Monday night, guidance indicates the front stalling and weakening near the Big Island. Immediately behind the front, there will be quite a noticeable airmass change with breezy north winds bringing in cooler and dryer weather. Dewpoints could drop into the mid to upper 50s Monday night for the smaller islands, with low temperatures dropping down into the mid 60s. Tuesday morning will start off chilly by Hawaii standards, but should be a fair weather day with plenty of sunshine across the smaller islands. Some lingering moisture will be possible across windward Big Island on Tuesday.
Starting Wednesday, both the GFS and ECMWF bring yet another cold front down to approach the islands from the northwest. This front looks to be stronger than the first front with breezy to strong Kona winds developing ahead of the front. Both models agree on timing with the front and move it quickly down the island chain Wensday night through Thursday night. With the front being stronger, we could see periods of moderate to locally heavy showers along the frontal boundary. Once again, a cooler and dryer airmass will follow behind the front with high pressure building back in on Friday.
A trough of low pressure lingering north of the state has allowed for some lingering low clouds and isolated showers this morning for a few areas across the state. For today, sea breezes will once again develop by late morning and will allow for interior clouds and some scattered showers this afternoon. Any showers should diminish this evening with the loss of diurnal heating and the development of the offshore land breezes. VFR conditions should prevail today with brief periods of MVFR conditions possible with any showers.
No AIRMETs in effect.
A weak high pressure ridge will remain nearly stationary over the central waters as a front dissipates over northern waters today. Another cold front will sweep from west to east down the island chain on Monday, stalling near the Big Island by Monday night. An even stronger cold front will quickly move through the islands, spreading strong to near gale force winds across the northwestern coastal waters late next week from Wednesday into Thursday. A Small Craft Advisory was issued for Hawaiian Coastal Waters exposed to the large northwest swell, these elevated seas above 10 feet are forecast to last at least the overnight hours for waters and channels exposed to this rising northwest swell.
A large northwest swell building through Hawaiian coastal waters today will increase surf heights above advisory thresholds. A High Surf Advisory (HSA) was issued this morning for exposed north and west facing shores. Offshore buoy reports this morning at buoy 51001 and 51101, show quickly rising seas from this next large northwest (310-330 degree) swell with advisory level surf on the way. Surf heights will swiftly increase through the day for all islands exposed to this rising northwest swell. Swell energy will then hold above HSA thresholds into Monday as another much larger overlapping northwest (320-330 degree) swell swiftly builds surf to High Surf Warning levels potentially from Monday through Tuesday. Yet another XL swell will build into the islands by late Thursday, potentially producing another round of warning level surf along exposed north and west facing shores.
Surf along east facing shores will remain small through the weekend as winds over and upwind of Hawaii remain weak. Some increase in east shore surf is possible early next week as a cold front moves down the island chain. Along south shores, surf will remain very small through the forecast period.
High Surf Advisory until 6 PM HST Sunday for Niihau-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Kauai East- Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.
Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters.
