Prognostic Meteorological Discussion
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FXHW01 KWNH 231216
PMDHI

HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
815 AM EDT WED AUG 23 2017

VALID 00Z THU AUG 24 2017 - 00Z THU AUG 31 2017

SURFACE HIGH PRESSURE NORTH OF THE STATE IS FORECAST TO ALL
GUIDANCE TO GRADUALLY WEAKEN OVER THE NEXT SEVERAL DAYS AS A BROAD
AREA OF NEGATIVE HEIGHT ANOMALIES DEVELOPS ACROSS THE NORTH
CENTRAL PACIFIC. BY THE MIDDLE OF NEXT WEEK, MODELS GENERALLY SHOW
SOME DEGREE OF RIDGING REESTABLISHING ITSELF NORTHEAST OF THE
HAWAIIAN ISLANDS, RESULTING IN A BROAD MID/UPPER-LEVEL BLOCKING
PATTERN ACROSS THE NORTH AND CENTRAL PACIFIC. THE WEAKENING
SURFACE HIGH NORTH OF THE ISLANDS SHOULD RESULT IN A SLIGHT
WEAKENING OF THE TRADES THROUGH EARLY NEXT WEEK. A RELATIVELY DRY
AIR MASS ADVECT ACROSS HAWAII INITIALLY, WITH PRECIPITABLE WATER
VALUES DECREASING INTO THE 1.00-1.30 INCH RANGE, WHICH SHOULD
SUPPRESS SHOWER ACTIVITY TO A DEGREE. A TROPICAL WAVE IS EXPECTED
TO PASS SOUTH OF HAWAII SUNDAY AND MONDAY, WHICH COULD RESULT IN A
MOISTURE INCREASE PRIMARILY FOR THE BIG ISLAND (PWATS INCREASING
TO 1.7-2.00 INCHES PER THE 00Z ECMWF, A BIT LESS PER THE 06Z GFS).
THUS, EXPECT THE POTENTIAL FOR AN INCREASE IN SHOWER ACTIVITY
ACROSS THE BIG ISLAND BY SUNDAY OR MONDAY. IN THE WAKE OF THIS
MOISTURE SURGE, EASTERLIES SHOULD PICK UP A BIT, AS THE RIDGE
REESTABLISHES ITSELF NORTHEAST OF HAWAII.

RYAN

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