Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
701 FXHW60 PHFO 170125 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 325 PM HST Mon Sep 16 2024 .SYNOPSIS... Locally breezy trade winds will continue to bring humid and somewhat wet conditions tonight, especially for windward areas. Drier trade wind weather will prevail Tuesday into the weekend, with moderate showers focused over windward slopes. && .DISCUSSION... After a very wet night for most windward areas, diurnal trends led to a significant decrease in rainfall by mid-morning, and during the past 3 hours, only a few stations on Kauai have registered more than a quarter of an inch of rain. Isolated heavy showers are flaring on the upper slopes of Mauna Loa this afternoon, but other leeward areas have seen little shower activity today. The fuel for the rainfall is moisture accompanying a mid-level trough that is drifting westward over the island chain. Precipitable water remains quite high, between 1.6 to 2 inches based on satellite and sounding data, and an increase in shower frequency is expected over windward areas tonight. With some drier trade wind flow moving in from the east and undercutting the moisture, rainfall totals should be significantly less than last night. However, expect humid conditions to linger as dew points remain elevated in the low to mid 70s. The deeper moisture will move off to the west on Tuesday, bringing a less active shower pattern. Surface high pressure north of the state will drive moderate to locally breezy trade winds, with a brief decline in the trades possible around Thursday and Friday. While a ridge aloft will bring stability, the mid- level trough will linger nearby into Wednesday, which will keep shower chances a bit higher than normal. However, dew points will fall into the upper 60s over most leeward areas, bringing some relief from the humidity. Drier conditions are due Thursday and Friday and likely into Saturday. While a ridge aloft will maintain stability over the islands through much of the week, an upper-level trough will persist to the west. The main effect of this feature will be periods of high clouds overhead. Models suggest that a low aloft may develop Sunday and Monday and north of Kauai. At this time, it does not look like it will affect local weather significantly. && .AVIATION... For the windward terminals expect scattered showers bringing temporary MVFR conditions through tonight and early Tuesday morning. Elsewhere and otherwise, VFR conditions are expected to prevail. With locally breezy trade winds prevailing across the state, AIRMET Tango remains in effect for low-level turbulence over and downwind of terrain. This AIRMET will likely continue through Tuesday. && .MARINE... Moderate to locally strong trade winds will continue through Wednesday as strong surface high pressure remains to the north northeast of the islands. Winds are then expected to decrease slightly to moderate levels after Wednesday as the surface high pressure slightly weakens and moves east. A Small Craft Advisory (SCA) is in effect for all waters surrounding Maui County and the Big Island through tonight, and then the typically windy waters around the Big Island and Maui County through Tuesday night. The SCA may need to be extended through Wednesday. Surf along east facing shores will remain choppy through Wednesday, then decrease thursday and Friday as trade wind speeds decrease. Surf across the other shores will be below seasonal averages through the week. A small southwest pulse out of the Tasman Sea could produce a slight rise in surf Friday. Aside from trade wind wrap, surf along north facing shores will be minimal through Wednesday, and a tiny northwest swell will be possible Thursday or Friday. Then a slightly larger northwest swell will be possible by late Monday next week. The combination of seasonally high astronomical tides and water levels running around 6 inches higher than predicted will produce localized coastal inundation through Tuesday afternoon. A Coastal Flood Statement has been issued to highlight these conditions. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Tuesday for Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters. Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Brenchley MARINE...JVC/Tsamous