609
FXHW01 KWNH 050640
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 AM EDT SUN APR 5 2026
VALID 00Z MON 06 APR 2026 - 00Z MON 13 APR 2026
...HEAVY RAIN AND FLASH FLOODING POTENTIAL INCREASING MID TO LATE
WEEK...
CONFIDENCE CONTINUES TO INCREASE REGARDING A HEAVY RAINFALL AND
POTENTIAL FLASH FLOODING THREAT FOR THE MID TO LATE WEEK PERIOD.
BUT FIRST IN THE SHORT TERM, A TRANQUIL PERIOD WILL PERSIST
THROUGH MONDAY AS SURFACE HIGH PRESSURE REMAINS ESTABLISHED NORTH
OF THE STATE, MAINTAINING A DRY AIRMASS AND BELOW-AVERAGE
PRECIPITABLE WATER (PW) VALUES. HOWEVER, THE SYNOPTIC PATTERN
BEGINS TO SHIFT SHORTLY THEREAFTER AS THE FIRST OF TWO UPPER-LEVEL
TROUGHS CROSS THE DATELINE, WITH SHORTWAVE ENERGY APPROACHING THE
ISLANDS FROM THE NORTHWEST MONDAY INTO TUESDAY. WHILE THE
ASSOCIATED COLD FRONT IS EXPECTED TO REMAIN WELL WEST OF THE
ISLANDS, LOW-LEVEL WINDS WILL VEER SOUTHERLY AHEAD OF THE
BOUNDARY, SUPPORTING THE RETURN OF DEEPER TROPICAL MOISTURE ACROSS
THE STATE BEGINNING TUESDAY.
PW ANOMALIES WILL INCREASE FURTHER THROUGH MIDWEEK AS A SECOND,
MORE POTENT UPPER-LEVEL TROUGH MOVES EAST OF THE DATELINE AND DIGS
TOWARD THE ISLANDS. GUIDANCE INDICATES THAT A SURFACE LOW WILL
DEVELOP AND STRENGTHEN ALONG THE LINGERING BOUNDARY AS AN UPPER-
LEVEL LOW BEGINS TO CLOSE OFF NORTHWEST OF THE ISLANDS BY
THURSDAY. THIS EVOLUTION IS EXPECTED TO SIGNIFICANTLY AMPLIFY THE
SOUTHERLY FLOW, DRAWING A DEEP PLUME OF TROPICAL MOISTURE OVER THE
STATE AND INCREASING THE POTENTIAL FOR ORGANIZED HEAVY RAINFALL
AND FLASH FLOODING. ENSEMBLE GUIDANCE CURRENTLY REFLECTS THIS
INCREASING THREAT; BOTH THE GFS AND ECMWF ENSEMBLES SHOW
PROBABILITIES EXCEEDING 60 PERCENT FOR 24-HOUR RAINFALL TOTALS
OVER ONE INCH FOR THE WESTERN ISLANDS, WITH THE ECMWF ENSEMBLE
HIGHLIGHTING OVER A 40 PERCENT CHANCE FOR AMOUNTS OVER TWO INCHES
THURSDAY INTO FRIDAY. WHILE MODEL DIVERGENCE EXISTS REGARDING THE
EXACT TRACK AND TIMING, THE GENERAL CONSENSUS SUGGESTS THE LOW
WILL EVENTUALLY WEAKEN AND LIFT NORTHEASTWARD. HOWEVER, A SURFACE
BOUNDARY AND ITS CORRESPONDING AXIS OF DEEP MOISTURE ARE LIKELY TO
REMAIN DRAPED OVER THE ISLANDS, SUSTAINING A HEAVY RAIN AND
FLOODING THREAT THROUGH THE WEEKEND.
PEREIRA
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