555
FXHW01 KWNH 190720
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 AM EDT SUN APR 19 2026
VALID 00Z MON 20 APR 2026 - 00Z MON 27 APR 2026
THE SYNOPTIC PATTERN ACROSS THE CENTRAL PACIFIC IS FORECAST TO
REMAIN PROGRESSIVE THROUGH THE UPCOMING WEEK AS THE STATE
TRANSITIONS FROM AN ACTIVE TROUGHING REGIME TO INCREASED
RIDGING WITH SURFACE HIGH PRESSURE BUILDING IN FROM THE NORTH-
NORTHEAST. INITIAL MODERATE TRADE WINDS ARE EXPECTED TO WEAKEN AND
VEER TO THE SE-S-SW, PARTICULARLY ACROSS THE WESTERN END OF THE
ISLAND CHAIN, AS LOW PRESSURE DEEPENS SEVERAL HUNDRED MILES
NORTHWEST OF KAUAI. ALOFT, A SHARP UPPER-LEVEL TROUGH DIGGING
SOUTHWARD WILL PROVIDE SUFFICIENT UPPER-LEVEL SUPPORT TO ENHANCE
INSTABILITY AND INCREASE HIGH CLOUD COVER THROUGH MONDAY. MODEL
GUIDANCE REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EVOLUTION OF
THIS TROUGH, THOUGH SUBTLE DIFFERENCES EXIST IN THE DEPTH OF THE
ASSOCIATED MOISTURE PLUME. A BLEND OF THE GFS AND ECMWF IS PREFERRED,
AS BOTH INDICATE A PERIOD OF INCREASED CONVECTIVE POTENTIAL.
IN THE SHORT TERM (DAYS 1-3), LIGHT WINDS WILL ALLOW FOR THE
DEVELOPMENT OF LOCALIZED LAND AND SEA BREEZE CIRCULATIONS. THIS
REGIME WILL FAVOR CHANCES FOR ISOLATED HEAVY SHOWERS AND EMBEDDED
THUNDERSTORMS MONDAY AFTERNOON AS THE UPPER TROUGH PASSES OVER THE
STATE, WITH THE ACTIVITY BECOMING FOCUSED OVER INTERIOR AND
LEEWARD AREAS DURING THE AFTERNOON TUESDAY AND WEDNESDAY. PWAT
VALUES ARE EXPECTED TO HOVER AROUND 1.5 INCHES THROUGH THURSDAY,
MAINTAINING A MOIST AIRMASS WITH THE POTENTIAL FOR HIGHER-
INTENSITY RAINFALL WHERE MESOSCALE CONVERGENCE IS MAXIMIZED.
IN THE LONG TERM (DAYS 4-7), MODEL GUIDANCE SUGGESTS A RETURN TO A
MORE STABLE TRADE WIND REGIME. SURFACE RIDGING NORTH OF THE STATE
BY THURSDAY AND FRIDAY WILL CAUSE TRADES TO REBUILD TO MORE
TYPICAL LEVELS. A SIGNIFICANT DRYING TREND IS FORECAST DURING THIS
PERIOD AS THE AIRMASS STABILIZES AND THE TRADE WIND INVERSION
LOWERS. PWATS ARE EXPECTED TO DECREASE TO BELOW 1.25 INCHES FROM
FRIDAY THROUGH NEXT WEEKEND. CONSEQUENTLY, PRECIPITATION COVERAGE
WILL SHIFT BACK TOWARD A STANDARD WINDWARD AND MAUKA FOCUS, WITH
SHOWERS CHARACTERIZED BY LIGHTER INTENSITIES AND LOWER OVERALL
COVERAGE. LEEWARD LOCATIONS SHOULD REMAIN MOSTLY DRY THROUGH THE
END OF THE PERIOD UNDER THIS BUILDING HIGH PRESSURE.
HURLEY
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page