Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans: Select a text product: Hawaiian Islands Synoptic Discussion and Guidance Hawaiian Islands Short Term Forecast Hawaiian Islands 7-day Zone Forecast Urgent Weather Message Marine Weather Statement/High Surf Advisory/Warning Special Marine Warning Radar Message Special Messages Terminal Aerodome Foreasts (TAFS) Area Forecast for Hawaii and Adjacent Coastal Waters AIRMETs for IFR Conditions, Turbulence, and Icing Hawaiian Islands Satellite Interpetation Message Oahu Surf Observation and Forecast/Coastal Forecast for Hawaiian Waters Offshore Forecast for Hawaiian Waters North Pacific High Seas Forecast South Pacific High Seas Forecast Hawaiian Islands Automated Surface Observation System Hourly Weather Roundup Hawaiian Islands Wind Data Hawaiian Islands Rainfall Summary Daily Hawaii Cooperative Observations East Pacific Tropical Weather Outlook West Pacific Tropical Weather Outlook Narrow the Menu List Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special Hawaiian Islands Synoptic Discussion and Guidance 664 FXHW60 PHFO 212017 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 1000 AM HST TUE MAY 21 2013 .SYNOPSIS... A WEAKENING LOW TO OUR NORTH AND A TROUGH JUST WEST OF KAUAI WILL KEEP WINDS LIGHT ACROSS THE STATE...LEADING TO ONSHORE SEA BREEZES DURING THE DAY AND OFFSHORE LAND BREEZES AT NIGHT. CLOUDS AND SHOWERS WILL BE FOCUSED ACROSS INTERIOR SECTIONS OF THE ISLANDS DURING THE AFTERNOON AND EARLY EVENING. AS THE LOW DISSIPATES...HIGH PRESSURE NORTHEAST OF THE STATE WILL BRING A RETURN TO TRADE WINDS BEGINNING THURSDAY. TRADES WILL STRENGTHEN THROUGH THE WEEKEND. && .DISCUSSION... WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW ABOUT 600 MILES NORTH NORTHEAST OF THE STATE...WITH AN UPPER TROUGH EXTENDING ABOUT 300 MILES NORTHWEST OF KAUAI. AT THE SURFACE...LOW PRESSURE IS LESS THAN 500 MILES NORTH OF KAUAI...WITH A TROUGH PASSING JUST WEST OF THE ISLAND. A WEAKENING FRONT IS ALSO NEARLY STATIONARY NORTHEAST OF MAUI COUNTY AND THE BIG ISLAND. 12Z RAOB SHOW ELEVATED INVERSIONS NEAR 9-10KFT...WITH A WEAKER INVERSION AT HILO THAN LIHUE. PRECIPITABLE WATERS ALSO RANGE FROM 1.24 INCHES AT LIHUE TO 1.4 INCHES AT HILO. THIS LINES UP WELL WITH EARLY MORNING MIMIC TOTAL PRECIPITABLE WATER IMAGERY...WHICH SHOWS HIGHER MOISTURE VALUES EAST OF OAHU. WITH THE WEAK SURFACE FEATURES NEARBY...THE PRESSURE GRADIENT ACROSS THE ISLANDS REMAINS QUITE WEAK. THE PRESSURE DIFFERENCE BETWEEN BUOY 51101 TO THE NORTHWEST OF KAUAI AND BUOY 51003 TO THE SOUTH OF KAUAI IS AROUND HALF A MILLIBAR...WHICH IS 1MB LESS THAN THE LOW VALUES OBSERVED YESTERDAY. WIDESPREAD LAND BREEZES FORMED OVERNIGHT...AND ONSHORE SEA BREEZES ARE ALREADY BEGINNING TO DEVELOP THIS MORNING. THIS TYPE OF CONVECTIVE PATTERN IS EXPECTED TO CONTINUE THROUGH WEDNESDAY...WITH AFTERNOON CLOUDS AND SHOWERS AND SOME CLEARING AT NIGHT. A BAND OF HIGH CLOUDS HAS FILLED IN OVER THE SMALLER ISLANDS OVER THE PAST FEW HOURS AHEAD OF THE UPPER TROUGH...AND THESE CLOUDS WILL LIMIT INSOLATION INITIALLY. BASED ON MORNING SOUNDINGS... CONDITIONS ARE MORE UNSTABLE ACROSS THE EASTERN HALF OF THE STATE. ADDITIONAL MOISTURE IS LOCATED FARTHER EAST AS WELL...POOLED ALONG THE DISSIPATING FRONT. HOWEVER...CONVERGENCE ALONG THE WIDESPREAD SEA BREEZES SHOULD LEAD TO LIKELY POPS ACROSS THE INTERIORS OF THE ISLANDS THIS AFTERNOON. THE LOW NORTH OF THE STATE IS EXPECTED TO MOVE WESTWARD AND DISSIPATE...WITH THE SURFACE TROUGH MOVING FARTHER WEST OF KAUAI. THE GRADIENT REMAINS LIGHT THROUGH WEDNESDAY...WHICH WILL ALLOW FOR ANOTHER DAY OF ONSHORE SEA BREEZES AND AFTERNOON CLOUDS AND SHOWERS. DESPITE OFFSHORE LAND BREEZES TONIGHT...AS MAY SEE CLOUDS LINGER AS MOISTURE FROM THE FRONT SPREAD WESTWARD OVER THE STATE. THIS MOISTURE MAY ALSO HELP TO ENHANCE SHOWERS ON WEDNESDAY...DESPITE MORE STABLE CONDITIONS AND SLIGHTLY LOWER INVERSION HEIGHTS. HIGH PRESSURE NORTHEAST OF THE STATE WILL REASSERT ITSELF ACROSS THE ISLANDS BY THURSDAY. AS THIS HIGH MOVES SOUTHWARD AND THE RIDGE REESTABLISHES ITSELF NORTH OF THE STATE...WE SHOULD SEE STRENGTHENING TRADE WINDS THROUGH THE WEEKEND. HOWEVER...AN UPPER LEVEL LOW DEVELOPING TO OUR NORTHEAST WILL HELP TO DESTABILIZE THE AIRMASS BY THE WEEKEND. WHILE THE LATEST MODEL RUNS SHOW THIS FEATURE CONFINED TO UPPER LEVELS...WITH TRADES PERSISTING AT THE SURFACE...IT WILL HELP TO ERODE THE TRADE WIND INVERSION AND ENHANCE TRADE WIND SHOWERS. THIS PATTERN IS EXPECTED TO LINGER INTO EARLY NEXT WEEK. && .AVIATION... VFR CONDITIONS PREVAIL AT MOST OF THE TAF SITES WITH SOME LOCAL MVFR OCCURING OVER PHNY. THESE CONDITIONS WILL LIKELY PERSIST THROUGH MOST OF THE DAY. DAYTIME HEATING WILL CAUSE SOME MVFR CONDITIONS TO OCCUR MAINLY OVER INTERIOR AREAS THIS AFTERNOON DUE TO CLOUDS AND SHRA. && .MARINE... THE HIGH SURF ADVISORY FOR SOUTH FACING SHORES CONTINUES THROUGH THIS EVENING FOR THE PERSISTENT LARGE SOUTH SWELL. ELEVATED SURF FOR SOUTH FACING SHORES WILL LAST AT LEAST THROUGH WEDNESDAY. A MODERATE WEST-NORTHWEST SWELL IS EXPECTED TO ARRIVE TONIGHT AND PEAK WEDNESDAY INTO THURSDAY. WHILE THIS SWELL IS LARGER THAN NORMAL FOR THIS TIME OF YEAR...SURF IS EXPECTED TO REMAIN BELOW ADVISORY LEVELS FOR NORTH AND WEST FACING SHORES. TRADE WINDS ARE EXPECTED TO BE STRONG ENOUGH BY THE WEEKEND FOR SMALL CRAFT WIND CONDITIONS TO DEVELOP OVER THE WINDIER AREAS AROUND MAUI COUNTY AND THE BIG ISLAND. && .HFO WATCHES/WARNINGS/ADVISORIES... HIGH SURF ADVISORY UNTIL 600 PM HST THIS EVENING FOR SOUTH SHORES OF ALL ISLANDS. WIND ADVISORY IN EFFECT FOR BIG ISLAND SUMMITS UNTIL 6 PM HST THIS EVENING. && $$ PUBLIC/MARINE...BRAVENDER AVIATION...BURKE Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office This page is maintained voluntarily by the MKWC and the UHMET faculty, staff, and students. It was last modified on: Tue, Sep 21 2010 - 2314 UTC Send comments to: Ryan Lyman