Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
568 FXHW60 PHFO 061947 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 947 AM HST Mon May 6 2024 .SYNOPSIS... Breezy easterly trade winds will decrease to moderate levels by this afternoon. A weak upper-level disturbance will drift over the islands today, enhancing passing showers with a few thunderstorms possible over the Big Island. An unstable band of clouds and showers from an old front, followed by another, potentially stronger, upper trough moving into the region, will keep wet weather in the forecast lasting into the weekend. && .DISCUSSION... Current radar imagery shows scattered to numerous showers riding into the windward and mountain slopes of all islands this morning. Some of the stronger showers are drifting over into the drier leeward areas. Water vapor satellite imagery continues to show a weakening upper-level low slowly drifting from west to east across the island chain. This feature will produce enough instability to keep wet trade winds in the forecast today with isolated thunderstorms over the Big Island this afternoon/evening as it tracks eastward across the state. At the surface, a 1030 mb high remains far north of the island chain and will continue to produce breezy easterly trade winds across the state through the morning hours. Wind speeds will taper down through the day, becoming more moderate by this afternoon, as the high pressure system drifts eastward away from the state. Expect light to moderate easterly trade winds to continue through the rest of the week with a hybrid pattern of trade winds and sea/land breezes over terrain-sheltered leeward areas. Wetter than normal conditions remain in the forecast for all islands through the majority of this week. While Tuesday will trend a bit drier, wetter weather will return for Wednesday and Thursday as the remnants of an old East Pacific cold front drift into the islands on the trade winds. Global models continue to show an upper-level trough diving down over the state on Thursday and Friday, along with a surface trough reflection. The models still differ on the details, but this would keep enhanced showers in the forecast into the weekend, with the potential for some heavy downpours and chance of thunderstorms. Will continue to see how this scenario evolves over the next couple of days and refine the forecast as needed. && .AVIATION... Breezy easterly trade winds will persist through today, with clouds and showers favoring windward and mauka locations. MVFR conditions will be possible in any heavier showers. VFR conditions will prevail elsewhere. Although confidence is low, instability associated with an upper level low passing overhead could lead to an isolated thunderstorm or two over the Big Island this afternoon. AIRMET Tango is in effect for moderate turbulence aloft (FL280-FL380) as the tail end of an upper level jet streak stretches overhead. Conditions should improve by this evening as the upper level jet moves off to the east of the state. AIRMET Sierra may be needed this evening if shower and low level cloud coverage increase sufficiently. && .MARINE... Fresh to strong trade winds will slowly ease through Wednesday as a 1029 mb high nearly 850 nm north of the islands moves off to the northeast. A Small Craft Advisory (SCA) is in effect for the typically windy waters around the Big Island and Maui County, while borderline winds will remain in place elsewhere today. As winds decline to moderate to locally fresh strength late Tuesday, the SCA will be dropped entirely. A surface trough will form north of the state on Wednesday, and this feature may drift southward over the islands, leading to a disruption or further decrease in trade winds. Pulses of south to southwest swell are due this week, with High Surf Advisory (HSA) conditions expected by Thursday. The PacIOOS buoy off of Lanai is still showing some inconsistent energy in the 16 to 18 second range, but recent surf observations prompted a lowering of forecast surf on south shores through Wednesday. Forerunners from a larger and longer lived south-southwest swell will arrive Wednesday, and surf is expected rise to the HSA level during the peak of the swell Thursday and Friday. A small northwest swell will build today and persist through midweek. The NOAA buoys to the northwest are showing a swell of around 3 feet, while the swell at the Hanalei PacIOOS buoy has risen to over 2 feet at 15 seconds this morning. Expect this swell to continue to spread down the island chain today, peak Tuesday, and decline late Tuesday and Wednesday. Wind-driven waves of 7 to 8 feet at 8 to 9 seconds will maintain rough east shore surf above the May average today. As trade winds decline over the next few days, these seas will gradually decline to around May average by Tuesday, then drop to below average for the rest of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...TS AVIATION...Farris MARINE...Wroe