Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 AM EDT Sat Jun 20 2015 Valid 00Z Sun Jun 21 2015 - 00Z Sun Jun 28 2015 The latest guidance maintains good through period. Flow around an upper ridge to the northwest of the islands will bring a weak front/shear line toward the area during the weekend into Monday. This feature should be accompanied by a modest/brief weakening of trades that will likely be in the moderate range over the next week. Precipitable water values should reach or exceed 1.50 inches over the northwestern islands Sunday and Monday, which should provide some enhancement to typically windward shower activity. Continued eastward elongation of central Pacific surface high pressure behind the front should then encourage resumption of trades at a strength similar to that seen at the start of the forecast. By Thursday and Friday, the models and ensembles show a westward rebuilding of the upper ridge which may lead to a downstream trough/erosion of the subtropical ridge to the north of the islands. On Friday, the 06z GFS is little more amplified with the trough versus most other models and the ensemble means, though still within the full ensemble spread. Either way, an inverted surface trough near the 160th meridian on Friday with a slight re-enhancement in precipitable water values Thursday night into Friday morning which should provide some enhancement to typically windward shower activity before the easterly wave retreats to the west. Roth/Rausch