Monday 5 am Update – Hurricane Hilda

• WARNINGS: There are currently no coastal watches or warnings in effect. The National Weather Service says a tropical storm watch may be required for the Big Island later today or tonight. There is also a Hurricane Warning for the Hawaiian offshore waters beyond 40 nautical miles out to 240 nautical miles (this is different than a warning for land).
• LOCATION: Hurricane Hilda is 425 miles southeast of Hilo and is moving northwest at 9 mph. The National Weather Service says a turn toward the northwest and a decrease in forward speed is expected over the next 48 hours, with Hilda forecast to be moving very slowly on Tuesday and Wednesday.
• STRENGTH: Hilda is now a category one hurricane, with maximum sustained winds of 90 mph. Steady weakening is expected over the next 48 hours with Hilda forecast to weaken to a tropical storm on Tuesday.
• SIZE: Hurricane force winds extend outward up to 25 miles from the center and tropical storm force winds extend outward up to 70 miles.
• HIGH SURF: A High Surf Advisory is in effect for east facing shores. Waves will build to 6 to 10 feet today and rising to 8 to 12 feet tonight and early Tuesday.

National Weather Service at 5 am

LATEST SUBJECTIVE AND OBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES RANGE FROM 4.5/77 KT TO 5.0/90 KT. GIVEN THE FACT THAT HILDA’S SATELLITE REPRESENTATION HAS DEGRADED ONLY MARGINALLY OVER THE PAST 6 HOURS… THE INITIAL INTENSITY FOR THIS ADVISORY HAS BEEN LOWERED SLIGHTLY TO 80 KT. ANOTHER FLIGHT INTO HILDA WILL BE CONDUCTED BY THE U.S. 53RD WEATHER RECONNAISSANCE SQUADRON LATER THIS MORNING.

THE INITIAL MOTION VECTOR FOR THIS ADVISORY IS 300/08 KT… AS HILDA CONTINUES TO ROUND THE WESTERN EDGE OF A DEEP LAYER RIDGE CENTERED TO THE DISTANT EAST. HILDA IS EXPECTED TO GAIN LATITUDE OVER THE NEXT COUPLE OF DAYS AS IT ROUNDS THE RIDGE… BUT THE FORWARD SPEED IS FORECAST TO DIMINISH AS THE STEERING FLOW WEAKENS TODAY AND TOMORROW. AS HILDA MOVES NORTH OF THE RIDGE AXIS… IT WILL ENCOUNTER INCREASING WESTERLY WINDS ALOFT… ASSOCIATED WITH THE SUBTROPICAL JET STREAM. IN THE LATER PERIODS THE FORECAST ANTICIPATES THAT A MUCH WEAKER AND SHALLOWER HILDA WILL BEGIN TO MOVE TOWARD THE WEST-NORTHWEST WITH A GRADUAL INCREASE IN FORWARD SPEED AS IT IS STEERED BY THE LOW-LEVEL TRADE WIND FLOW.

THE 0600Z RUN OF THE GFS OFFERED A DRAMATICALLY DIFFERENT TRACK AND INTENSITY SOLUTION THAN PREVIOUS RUNS…WITH A MUCH WEAKER HILDA MOVING NEARLY DUE WEST OVER THE NEXT 3 DAYS AND PASSING WELL SOUTH OF THE BIG ISLAND BY TUESDAY NIGHT OR WEDNESDAY. THIS CONTRADICTS ECMWF GUIDANCE… WHICH SHOWS A FAIRLY WEAK HILDA MOVING NORTHWEST OVER WINDWARD WATERS OF THE HAWAIIAN ISLANDS BEFORE EVENTUALLY MOVING WEST NEAR KAUAI TOWARDS THE END OF THE WEEK. THIS RECENT DIVERGENCE IN SOLUTIONS FROM SOME OF THE MORE RELIABLE TRACK MODELS IS LIKELY DUE TO DIFFERENCES IN THE DEPTH OF THE FORECAST CIRCULATION… AND LEADS TO DECREASED CONFIDENCE IN THE OFFICIAL TRACK FORECAST. WITH THE SOMEWHAT DRAMATIC CHANGES NOTED IN RECENT MODEL RUNS… THE UPDATED TRACK FORECAST OFFERS LITTLE CHANGE FROM THE PREVIOUS.

THE INTENSITY FORECAST ALSO CONTAINS LITTLE SIGNIFICANT CHANGE FROM THE PREVIOUS… WITH STRONG VERTICAL WIND SHEAR LEADING TO A SIGNIFICANT WEAKENING OF THE CYCLONE THROUGH THE FORECAST PERIOD. THE WEAKENING TREND IN THE OFFICIAL FORECAST IS NOT AS RAPID AS INDICATED BY SHIPS… BUT STILL ANTICIPATES THAT HILDA WILL WEAKEN TO A TROPICAL STORM ON TUESDAY… SIMILAR TO THE IVCN CONSENSUS.

ALTHOUGH THE CURRENT FORECAST BRINGS HILDA NEAR THE BIG ISLAND AS A TROPICAL DEPRESSION LATER THIS WEEK… UNCERTAINTY REMAINS AS TO THE EVENTUAL IMPACTS THAT MAY BE FELT IN THE HAWAIIAN ISLANDS. INTERESTS IN HAWAII SHOULD CLOSELY MONITOR THE PROGRESS OF HILDA… AND A TROPICAL STORM WATCH MAY BE REQUIRED FOR THE BIG ISLAND LATER TODAY OR TONIGHT. IT IS IMPORTANT NOT TO FOCUS TOO CLOSELY ON THE EXACT TRACK AND INTENSITY FORECASTS BECAUSE AVERAGE INTENSITY ERRORS ARE NEAR 35 MPH ON DAY 5… AND AVERAGE TRACK ERRORS ARE NEAR 175 MILES. IN ADDITION… THE HAZARDS OF A TROPICAL CYCLONE CAN EXTEND OVER A BROAD AREA AWAY FROM THE CENTER.

FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 16.2N 149.8W 80 KT 90 MPH
12H 11/0000Z 16.8N 150.8W 70 KT 80 MPH
24H 11/1200Z 17.3N 151.6W 60 KT 70 MPH
36H 12/0000Z 17.8N 152.3W 45 KT 50 MPH
48H 12/1200Z 18.4N 153.2W 40 KT 45 MPH
72H 13/1200Z 19.0N 154.6W 30 KT 35 MPH
96H 14/1200Z 19.5N 156.0W 30 KT 35 MPH
120H 15/1200Z 20.0N 158.5W 25 KT 30 MPH…POST-TROP/REMNT LOW