Light to moderate trades with embedded showers favoring predominately windward and mauka areas are expected through the day, followed by drier and more stable conditions through the first half of the week. Winds will begin ease by Wednesday and veer southerly in response to an advancing front northwest of the islands. This front is expected to move over the islands during the latter half of the week, potentially increasing shower activity.
Latest radar data indicate the volcanic ash from Kilauea's Halemaumau Crater during episode 38 that started decreasing yesterday evening, has further decreased this morning. Radar observations as of 13z (3am HST LT) show the plume now at approximately 10000 feet mean sea level (MSL), with light ashfall possible southwestward within 5 miles from the volcano source.
Moderate trades continue to ease as an upper-level trough propagates into the vicinity of the islands. Latest satellite water vapor imagery clearly depicts a sub-tropical jet just north and west of Kauai producing two distinct upper-level lows; one on either side of the Hawaiian Islands. The more mobile low west of the islands will begin to dig southwestward away from the state, resulting in little impact. Conversely, the more intrusive, eastern low will result in a bit of instability, which may produce some brief enhanced shower activity focused over predominately windward and mauka areas.
Additionally, a well-defined band of moisture can be seen on satellite imagery is anticipated to bring showers mainly to windward areas of Big Island and Maui initially this morning. However, trends displayed on an American model (GFS) cross section of Hawaii portrays wetter conditions moving up the island chain to Molokai and Oahu late this morning to early afternoon. Overall precipitation accumulation will be on the lighter side, but some locations may fetch a tenth to upwards of a quarter of an inch of rainfall.
Model guidance of the GFS and European model (ECMWF) show the aforementioned low eventually strengthens and forms a closed low tomorrow, and slowly meanders away from the Hawaiian Islands. Ridging quickly builds in in its wake, allowing dry and stable conditions to return. This will open the doors to moderate trades reestablishing, with the more typical trade showers across windward and mauka areas with exception for the Kona slopes of the Big Island, where typical sea-breeze induced cloud buildups and showers will be possible during the day.
Toward the latter end of the week, model guidance introduces a front moving northwest to southeast. As this occurs, background surface winds will become light and veer southeasterly, allowing for daytime sea breezes and nighttime land breezes ahead of its arrival. There's still a fair bit of uncertainty with regards to the timing of the front, as the ECWMF displays a much earlier arrival time compared to the GFS. Furthermore, ECMWF shows the front to have a more modest impact to the Hawaiian Islands, dissipating apart much quicker. GFS, on the other hand, supports the likeliness of enhanced shower activity as it passes through. Further analysis will be needed to determine which scenario proves more favorable in the forecast guidance over the coming days.
Light to moderate trades will persist throughout the day and will bring periods of showers to windward and mauka areas. A band of moisture east of the islands will also move westward through the early portion of today, bringing enhanced showers, mainly across windward areas, but may trickle into the leeward and interior portions of the state. Brief MVFR conditions remain possible with passing showers. Otherwise VFR conditions prevail.
AIRMET Tango remains in effect for moderate turbulence between FL290-FL360 extending from Kauai to Maui.
A surface high pressure ridge will remain north of the Hawaii region, winds flowing around this ridge will produce gentle to moderate easterly winds today, then decreasing and veering more southeasterly to southerly from Tuesday to Wednesday as another cold front moves into the region from the northwest. A consensus of weather model guidance suggests this cold front may move into the western Hawaiian islands from late Wednesday into Thursday, then diminishing by Friday.
The current medium period north-northwest (340-350 degree) swell continues to slowly fade into Monday, bringing surf back down to below average levels for this time of year. The next two long to medium period overlapping northwest (310-320 degree) swell pulses will arrive on Monday and Tuesday, boosting surf along north and west facing shores and possibly reaching marginal advisory levels by Wednesday.
Choppy east shore surf will remain small and decline for the next few days as trades gradually ease. Expect minimal background energy for south facing shores keeping south shore surf heights above flat levels.
Peak monthly tides combined with water levels that are running higher than predicted will likely lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible through the peak high tide this morning.
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