textproduct: Honolulu

SYNOPSIS

High pressure far to our northwest will pass north of the islands Saturday, turning our cool northerlies to dry trades today. The high will move well northeast of the islands Sunday, causing local background winds to turn southeast. Humidity levels will be comfortably low through the holiday weekend. Very little, if any rainfall is expected for the next couple of days, but a small increase in mainly windward and mauka showers is expected after that. Our next cold front is expected to bring wet weather that will reach the islands around the middle of next week.

DISCUSSION

Cool and dry northerly breezes prevail across the main Hawaiian Islands early this morning. Sea level dewpoints are unusually low this morning, with some sites including Lihue and Honolulu as low as the upper 40s early this morning. Lingering moisture trailing the front had been bringing some persistent showers to portions of the Hamakua District overnight, but these have since faded as drier air takes over. The high res ensemble systems (HREF and REFS) both did a very nice job depicting this lingering moisture and resultant showers in that area last night.

The chilly post-frontal northerlies are thanks to a surface high roughly 600 miles NW of Kauai. The high will move fairly quickly eastward today, passing north of the main Hawaiian Islands on Saturday. This will swing the winds over to trades for today and Sat. The airmass is very dry and stable, so if there are any windward and mauka showers, they should be quite light. The vast majority of the area today should be rain-free. Both HREF and REFS show a very modest increase in trade wind showers Saturday as low-level moisture increases a bit, but still overall it should be rather dry.

The low level flow turns SE once again Sun into Mon as the surface high moves well NE of the islands, with a ridge extending to the SW across the islands. Overall, the airmass stays drier than normal and fine weather for the holiday weekend is expected with very limited shower activity.

The low level ridge over the islands will start to break down on Tue in advance of the next front. There is some variability in the models and ensembles about how light the winds will be be as they start to turn more southerly. At this point, moisture levels and moist-layer depth still look to be pretty meager for afternoon showers over the islands, so we should be limited to PM clouds and just a few sprinkles and probably not much more than that.

Models are in pretty good agreement bringing the next front to Kauai by Wed. There are some differences in the strength of this front, with the GFS showing a stronger, faster push down the chain with heavier showers. The ECMWF is not quite as strong, and slower. Our forecast shows an increase in showers at that time, but with the uncertainties in timing, did not get too fancy with depicting the cold front, and applied a blended approach to keep the PoP field rather broad for now. There perhaps could be some thunder associated with this front, but too much uncertainty in frontal timing and intensity to explicitly include for now.

AVIATION

Very dry and breezy NNE trades will steadily veer to NE through the day delivering limited clouds and perhaps a shower or two windward and mauka. A brief period of gusty N winds is possible Friday morning at PHTO before the gradient turns NE during midday. VFR areawide for the balance of the forecast period.

AIRMET Tango in effect for lee turb.

MARINE

A high pressure system to the northwest will move east for the next few days and bring stable breezy to locally strong trade winds. The northerly winds currently in place over the region will veer to the northeast and then east through Sunday. By late Sunday into early next week, winds are expected to weaken and veer southerly again ahead of another cold front. Current long range guidance shows this next cold front could approach the western coastal waters by the middle of next week.

An extra large northwest swell will maintain large seas today for exposed waters. A Small Craft Advisory (SCA) remains in effect for all Hawaiian waters through the afternoon for combined seas above 10 feet, and winds to 25 kt. After tonight, the SCA will be in effect over the eastern half of the islands for trade winds strengthening above 25 kt heading into the weekend.

An extra large, medium to long period northwest (320-340 degrees) swell which peaked earlier this morning will hold before declining this afternoon into the evening. A High Surf Warning remains in effect through today for exposed north and west facing shores of Niihau, Kauai, Oahu, Molokai, and north facing shores of Maui. Additionally, a High Surf Advisory is in effect for west facing shores of the Big Island. This swell will gradually transition to become more northerly (350-010 degrees) as it fades through the weekend. Surf along north and west facing shores will then linger near advisory levels Saturday before another reinforcing northwest swell arrives Sunday into Sunday night. This swell looks to bring surf heights above advisory levels. The swell will then gradually decrease through Monday before a WNW swell arrives Tuesday and peaks near advisory levels.

Surf along east facing shores will remain small, though will increase slightly today into the weekend as trades become re- established across the area. Additionally, some east facing shores sensitive to northerly swells may experience a slight uptick in surf heights this weekend as the fading northwesterly swell becomes more northerly. No noteworthy swells are expected for the next few days for south facing shores.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Warning until 6 pm HST for N and W facing shores of Niihau Kauai Oahu Molokai and N facing shores of Maui.

High Surf Advisory until 6 PM HST for W facing shores of the Big Island.

Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters.

Small Craft Advisory until 6 PM HST Saturday for Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.