An overall wet weather pattern will persist this week with bands of transient showers, some of which could be heavy at times, moving over the islands. Winds will be much lighter than those experienced within recent days, and will become variable through mid-week before southerly flow returns late this week. An additional period of heavy rainfall will be possible during the latter portion of this week as a new, but much weaker, Kona low develops near the islands.
This afternoon, deep moisture embedded within light to moderate southerly background flow across the eastern end of the state continues to stream over the Big Island and its surrounding waters, with fewer showers observed near east Maui. Pockets of heavy rainfall have fallen over portions of the Big Island throughout the day, including the Ka'u and Puna Districts late morning into early afternoon, followed by the North and South Kohala and Kona Districts as of mid-afternoon. For the remainder of the islands, much lighter and more isolated to scattered showers have occurred thus far today. However, additional convection can be seen developing on regional satellite and radar imagery at the western end of the state near Kauai as of press time, which has the potential to bring some localized heavy rain to the Garden Isle over the next few hours as well. All of these scenarios were decently well-supported in the hi-res guidance and HREF probabilities today. For this evening and tonight, bands of showers, some of which could be heavy at times, will continue to move across portions of the state, though the main one looks to be the westernmost band that will move southeastward throughout the night. Of note, we are not expecting anywhere near the significant impacts that were associated with the Kona storm late last week with this activity.
The High Wind Warning that was previously in effect for the Big Island summits and Haleakala has been downgraded to a Wind Advisory with this afternoon's updates. Based on the latest trends, it is possible that this advisory will be cancelled early, as wind speeds have quickly dropped within the past hour or so.
Current model solutions for Tuesday through mid-week maintain an upper-level trough across the region, supporting a pattern of light and variable winds with periods of occasional showers.
During the latter part of the week, confidence is increasing that another Kona low will develop west of the islands. Importantly, however, this low is expected to be considerably weaker than the most recent one, but could still be capable of delivering periods of heavy rain and flash flooding. Guidance indicates that winds will also not be as strong as the most recent storm, and are in fact expected be be unusually weak for a Kona low. It remains too early to determine which islands will be the most impacted at this time, and is also uncertain when the initial flooding threat may develop. With that said, the forecast for the extended period has undergone significant updates with this afternoon's forecast package, mainly to include adjustments to the location, timing, and magnitude of rain chances from Thursday into the weekend. Given the uncertainty at this range, the forecast will continue to be refined in subsequent updates.
Showers continue to bring intermittent MVFR and IFR to PHKO on the Big Island this afternoon and tonight. A separate band of showers moving in from the west will begin to impact PHLI later this afternoon and into tonight as a surface trough moves into the state. This band of showers will move through Kauai, Oahu, and Maui before reinforcing the showers on the Big Island Tuesday. Occasional MVFR is forecast, and isolated IFR will continue to occur.
AIRMET Sierra remains in effect for mountain obscuration for Maui, Lanai, and the Big Island. Conditions have not been improving as much as previously expected, and this AIRMET may need to be extended.
The gradient will remain rather weak through Wednesday, with light and variable winds prevailing over the waters. A brief period of light to moderate trades will be possible Thursday as a weak ridge builds north of the state, followed by light to moderate S winds on Friday as a new system approaches from the west.
Surf along S shores is trending down as S to SW winds ease. A new long period south swell will then arrive late tonight and Tuesday giving an extended boost to S shore surf through late this week.
A moderate short-period W swell associated with the recent Kona storm is affecting N and W facing shores today, but surf remains below the advisory threshold. The short-period W swell will lower tonight and Tuesday while a new medium-period NNW swell fills in. This NNW swell could elevate surf to near the advisory threshold Tuesday night and Wednesday. The swell then shifts more N and lowers Thursday into the weekend.
Surf along E facing shores will remain well below normal through late week as trades over and upstream of the islands remain disrupted.
Wind Advisory until 6 PM HST Wednesday for Haleakala Summit-Big Island Summits.
