Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 714 AM EST Sun Dec 23 2018 Valid 00Z Mon Dec 24 2018 - 00Z Mon Dec 31 2018 ...Heavy Rainfall Threat Later Week... A favored composite of reasonably clustered model and ensemble guidance indicates that high pressure northeast of the islands will continue to favor seasonal Hawaiian trades over the next couple of days in a pattern with windward showers. Wetter flow is expected to develop across the state by Christmas as deeper moisture returns to the state. This occurs as shortwave trough passages to the north interact with a retrograding upper level low that works underneath over the state. In this pattern a cold front approaches from the northwest and lead trade flow relaxes. This developing wet pattern may be further enhanced Friday through next weekend as another pooling moisture front is expected to work across the islands from the northwest coincident with amplification and approach of a mid-upper level trough with potential closed low development over the state. The 06 UTC GFS/GEFS mean are trending stronger with this feature, but are still less amplified than the 00 UTC ECMWF/UKMET/Canadian and ECMWF ensembles. Upstream mid-upper level ridge amplitude seems to favor the more amplified cluster of solutions and that scenario would set the stage for widespread heavy rainfall/convection along with the threat of runoff problems in an increasingly unstable pattern. Schichtel