Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 818 AM EDT Wed Mar 21 2018 Valid 00Z Thu Mar 22 2018 - 00Z Thu Mar 29 2018 Typical detail uncertainties persist but guidance continues to agree in principle on a pattern that should be favorable for a heavy rainfall threat this weekend. An upper trough approaching from the west late in the week will likely pull abundant deep moisture into the area from the southwest with precipitable water values possibly approaching or reaching two inches at some locations Saturday and possibly extending into Sunday depending on speed of the system. In addition there continue to be indications of an accompanying surface trough/embedded waviness that would provide an added focus for rainfall. Overall the Saturday-Saturday night period has higher confidence for heavy rainfall with timing differences becoming evident by Sunday (00z/06z GFS slower than the 00z ECMWF and UKMET/CMC leaning faster than the GFS/ECMWF average). The upper trough should pass overhead by Monday with flow aloft gradually trending west-southwesterly as a deep trough develops over the central Pacific by the middle of next week. Expect any shower activity during the first half of next week to be on the lighter half of the spectrum with some land/sea breeze influence given persistence of an ill-defined surface pattern. In the shorter term, expect brisk winds from the east or southeast around the periphery of east-central Pacific high pressure along with a tendency for windward focus of showers. Most guidance continues to suggest that the ECMWF may be a bit overdone with the eastward extent of heavier rainfall near the western islands from now into Friday. Rausch