A high pressure system will remain in place north of the Hawaiian Islands through the weekend keeping moderate to locally breezy trade winds into the extended range forecast. A disturbance passing through the islands today will briefly increase shower activity through the morning hours. More stable conditions with limited shower activity returns into Friday. Another upper level disturbance moves over the islands producing a slight increase in shower activity forecast from Friday afternoon through the weekend.
An easterly wave moving through the islands shows up on this mornings satellite imagery as unstable cloud bands moving through the central and western islands. More stable stratocumulus clouds are filling in behind this trough as the ridge builds over the state and we return to more stable weather conditions later today. Local radar imagery shows scattered to numerous shower bands drifting into the windward and mountain slopes of each island on the trade winds. A few of the strongest showers may bring brief showers to the typically drier leeward areas.
After a wet summer morning, expect drier and more stable conditions to develop across the state lasting into Friday, as high pressure will keep a subsidence cap on vertical cloud development. Subtle changes in the island cloud and shower pattern will become less stable from late Friday on into the weekend, as a weak upper level low injects some instability across the Hawaii Region. A slight increase in shower trends are anticipated mainly during the overnight to early morning hours favoring the windward and mountain areas.
Confidence in these shower trends remain moderate at this time, as the strength of the upper low is currently projected to be on the weaker side of the equation. More details will become clearer later this week, as the time period grows closer, and our confidence on island by island shower trends improve.
A high pressure ridge remains in place north of the Hawaiian Islands this week. Moderate to locally breezy easterly trade winds remain in the forecast. Shower trends will remain elevated this morning as a low level trough passes westward through the island chain. Periods of MVFR conditions are expected in any showers, especially affecting windward airfields. Weather conditions will trend to the stable side through the day with limited clouds and showers through the week.
AIRMET Sierra for mountain obscuration remains in effect for north and east slopes of most islands.
A ridge of high pressure will remain far north of the state throughout the week. Trades should gradually strengthen today. A Small Craft Advisory (SCA) is in effect for the typical windy areas around Maui County and the Big Island starting 6AM this morning. Fresh to locally strong trades will likely persist through most of the week, although we could see winds drop below SCA criteria as a weak trough develops over the western end of the state into the weekend.
Surf along south facing shores should see a small boost over the next few days due to a pair of south and south-southeast swells. A long-period south swell should peak today near summer averages. As this swell declines a reinforcing swell from the south- southeast should fill in later today into Wednesday. This should maintain surf heights through the middle of the week. Surf should gradually decline Thursday into Friday, but another small increase is expected into the weekend as a new long-period southwest swell arrives from the Tasman Sea.
Surf along east facing shores will continue to remain rough and choppy with surf heights getting a slight increase as the trades strengthen. Surf along north facing shores will continue to decline through Wednesday.
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
