Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 729 AM EST Sat Nov 24 2018 Valid 00Z Sun Nov 25 2018 - 00Z Sun Dec 02 2018 Upper-level ridging will persist across Hawaii through the next several days before things begin to change by the mid to late part of next week. A surface cold front is expected to weaken as it pushes south toward Hawaii Mon-Tue, with little to no impacts in terms of sensible weather for the islands. Trades will gradually strengthen slightly into the 15-20 kt range through Wed. After that time, confidence continues to grow that a wave in the westerlies will develop across the Central Pacific early next week, which will then undergo significant amplification as it approaches Hawaii by late in the week, with a surface low pressure system likely to track several hundred miles northwest of the state. There remains some uncertainty as to the exact degree of amplification that will occur, with the UKMET the least amplified solution and the ECMWF the most amplified. At this point, solutions seem similar enough that a blend/consensus approach is likely best. Given the expected evolution of this system, the stage will be set for northward transport of moisture from the deep tropics, and the potential for heavy rain for Hawaii. Ensemble probabilities are likely the best indicator of heavy rain potential at this point given the time frame and the range of possible solutions. Current ECENS probabilities show low-moderate confidence at this point, with 48-hour probabilities of exceeding 1 inch of rainfall in the 20-30 percent range for the western islands Thu-Sat, with probabilities decreasing farther east. Future model/ensemble runs over the coming days will add more confidence in the specifics of this system and the degree of any heavy rainfall threat that exists for late next week. Ryan