textproduct: Honolulu

SYNOPSIS

Moderate to locally breezy trades will occur the next several days. Stable and generally dry conditions as infrequent isolated windward and upslope mauka showers quickly pass through to the west. Drifting Tropical Storm Lowell far southeast of the state and is forecast to resume a westerly track this weekend. Lowell will likely be approaching the islands from the east southeast through next week.

DISCUSSION

Upper and mid level ridging has asserted enough influence across the Central Pacific to still provide the needed subsidence to result in continued warm and dry weather, with only isolated early day windward showers. A large area of 1034 mb surface high pressure located far north of the state is creating a tight enough pressure gradient, in relation to lower equatorial pressure, to result in persistent moderate to locally breezy trade winds. The next few days will feel less humid and generally more pleasant under this moderate trade flow.

The lower levels remain void of any significant features that would indicate any short term deviation from the recent pattern. Morning soundings indicate a 6-7k ft inversion layer depth that is deep enough to support mainly isolated showers. Locally stronger winds gusting to near 25 to 30 mph will occur atop higher terrain ridgetops and through lee valleys and/or slopes. These amped up trades will hang with us through early next week with a potential approaching tropical cyclone being a disrupter to what will be several days of breezy trades. Most diurnal rain accumulation will measure in the hundredths of an inch. Greater rainfall will likely focus across windward upslope areas. Recent regional sounding profiles indicate that mid to upper ridging will remain in control helping to maintain dry mid-levels (20-40% %RHs between 8-15k ft). This scenario will result in less frequent windward exposure showers. Quick-hitting light showers trapped within the trade belt will likely be more recurrent during the nocturnal hours than during the day. The rapid nature of these cells passing over high terrain will have better organized showers wetting leeside communities. The weather pattern will turn more wet going into the middle of next week as higher moisture reaches greater depths as weak ridging slides westward.

The National Hurricane Center is issuing forecast advisories for Tropical Storm Lowell. Long-range models show Lowell will advance toward the state next week. As no distinct center of circulation has appeared with Lowell and it has been drifting, deterministic model guidance have struggled with grabbing onto this system and therefore have lacked any run-to-run consistency. Ensemble members that move Lowell in close vicinity of the island chain in a little over a week still remain in the minority. Google Deepmind's ensemble takes the storm due west then northwest into a less sheared environment south of Hawaii over the Labor Day Weekend.

AVIATION

For 12Z - rinse and repeat under moderate trades regime. Mostly VFR overnight with some MVFR conditions with passing showers/lower CIGs. Expect low CIGs and SHRA over windward and mauka slopes most areas and reflected as VCSH most TAFs. MVFR conds in heavier SHRA, otherwise VFR prevails.

AIRMET Tango is in effect for mod low-level turb lee of terrain and may be needed for a few days.

MARINE

A tight pressure gradient between a 1034 mb surface high located about 1,400 nautical miles north of the islands and relatively lower equatorial pressure is resulting in regional moderate to locally strong trade winds. Little change in this pressure orientation will guarantee fresh magnitude winds the next several days. A Small Craft Advisory remains in effect for the windier waters surrounding Maui County and Big Island and will likely remain in effect over those waters into early next week.

South-facing shore surf will hold just below advisory levels today as an ongoing small to moderate size, medium period south southwest swell continues to pass around the islands and fades through the weekend. A similar size south swell is expected to arrive during the middle to the latter half of next week.

Short period chop will keep east-facing shore surf rough in response to the recent moderate to fresh trades over and upstream of the islands. Eastern shore chop may be enhanced by the arrival of a small, medium period east swell originating from former Tropical Storm Iselle. This swell will begin to fill in today, peak Saturday before slowly fading early next week. Tropical Cyclones Karina and Lowell will generate captured east fetches that may pass around the state mid to late next week. This will strictly be dependent upon these cyclones' future track and intensity.

FIRE WEATHER

Relatively dry regional air and moderate to locally breezy trade winds will maintain moderate fire weather concerns into early next week. A slight increase in moisture next week will marginally improve conditions.

HFO WATCHES/WARNINGS/ADVISORIES

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