Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 808 AM EDT Mon May 25 2015 Valid 00Z Tue May 26 2015 - 00Z Tue Jun 02 2015 Guidance is agreeing in principle with a retrogression of the east-central Pacific mean trough. With respect to individual features this plays out as a leading trough/upper low is currently being ejected by another system settling to the north-northeast of the state Tue-Fri. Then a somewhat flatter trough should reach a position to the north of the region by the start of next week. This evolution will encourage an increase in deep moisture/rainfall potential, with precipitable water values starting out in the 1-1.25 inch range and trending toward at least 1.25-1.50 inches. Based on the current array of 00z GEFS/ECMWF ensemble members, there is a decent possibility that PWATs may exceed 1.50 inches at least briefly sometime within the Thu-Mon period. However the 1.75-2 inch values in the 06z GFS by next Mon are extreme versus the 00z ensemble envelope. During the first half of the period generally northerly/northeasterly winds should lighter thus allowing land and sea breeze boundaries to have more influence on shower activity. Also most guidance is suggesting a surface trough may become established over the islands and provide an added focus for rainfall. Late in the period surface high pressure building toward the central Pacific may help to flatten the surface pattern over the islands a little and bring a return to more typical trades. By Sun-Mon the 00z ECMWF/CMC and GEFS/ECMWF means are most similar in depicting this idea while the less favored 00z/06z GFS hold onto a more pronounced inverted surface trough. Rausch