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North Pacific high
Kenwood Cup yachts in Honolulu get a wake up call as races cancelled ... thanks to no wind at all! August 2, 2000 Tropical Storm Daniel gave the world's best skippers a 'heads-up' this week when Tropical Storm Daniel slipped across the Hawaiian island chain, disrupting the already light trades to bring a surprisingly windless first day to the Kenwood Cup. Sustained winds of 70 knots close to the storm, however, created messy surf and localised flooding for the north shore of Oahu. Daniel is one of the largest storms to brush past the Hawaiian Islands since Hurricane Iniki caused major devastation on Kauai in 1992.
Where's the Pacific High? This is the hurricane season, but generally the islands are protected by the dominating influence of the Pacific High pressure cell, centred to the north of the islands. Hawaii at this time of year is typically bathed in trade winds, although race conditions at the last Kenwood cup, two years ago, were also hampered by light winds. Then it was thanks to the remnants of Tropical Storm Estell which worked against the normally reliable Trade Winds. Tropical storm Daniel, late on July 31 shown at its strongest point, packing sustained winds of 70 knots close to the centre. Off Honolulu, however, a practice race as part of the Kenwood Cup saw yachts drifting on a glassy sea as weak surface trades from the north east were all but extinguished by winds circulating counter-clockwise around Daniel. From here the storm moved slowly to the north west and lost oomph. Cyclones are not unusual in Hawaii, but neither are they common. For another view of Daniel affecting surface trade winds, click here. Image courtesy of Tropical
Cyclones group, What's going on? According to Kevin Kodama, of the Central Pacific Hurricane Center Normally, the Northeast Pacific High keeps tropical cyclones on a well-behaved, roughly east to west track. In the case of Daniel, the high and an associated ridge of high pressure were too weak to prevent its movement into the region. This, combined with an upper level trough, helped drive it toward the northwest. This was particularly so when thunderstorms were active in the hurricane itself, as Kodama points out. "Whenever thunderstorms died down, the center of the hurricane tracked more due west." he said. "When they flared up, the center moved northwest. This made the track forecast extremely challenging because the intensity fluctuations also changed the movement of the storm." No stranger to Hawaiian waters Patrick Caldwell, meteorologist with NOAA/NODC at Honolulu, points out that Daniel's presence is not unusual. "Tropical activity off Mexico moves in our direction," he says. "Some depressions maintain their intensity if they don't get their tops blown off from wind shear. Daniel made it here intact.". Caldwell points out that the North Pacific High is already filling back in and Daniel is now 'out of the picture'. Storm notes July 31, Hawaiian time: STORM INFORMATION.. AT 11 AM HST...DANIEL WAS CENTERED 150 MILES EAST OF KAHULUI...OR 245 MILES EAST OF HONOLULU AND MOVING JUST NORTH OF WEST AT 8 MPH. MAXIMUM SUSTAINED WINDS ARE NEAR 70 MPH WITH HIGHER GUSTS. THE EFFECTS OF DANIEL ARE EXPECTED OVER MAUI COUNTY LATE TONIGHT AND OAHU ON TUESDAY. SURF HEIGHTS BETWEEN 8 AND 12 FEET...COMBINED WITH HIGH TIDES AND STORM SURGES BETWEEN 2 AND 4 FEET...MAY CAUSE LOCALIZED FLOODING AND EROSION ALONG EAST FACING SHORES. WINDS MAY RANGE BETWEEN 40 AND 50 MPH. THESE WINDS CAN CAUSE DAMAGE TO VEGETATION AND SOME STRUCTURES...AND ARE USUALLY STRONGER WHEN BLOWING DOWNSLOPE. As it turned out, winds failed to materialise as Daniel kept well offshore, but it provided meteorologists with some food for thought, as one local surf forecaster explains: Pat Caldwell's surf and wind forecast for Oahu for July 31 - "Daniel lost its symmetrical shape and gradually its intensity yesterday (July 30) and last night due to its interaction with the weak weather feature to our immediate north. As seen from the color enhanced infrared satellite photos, the high clouds were being pulled northeastward by the SW winds associate with an upper level trough. This shearing had a weakening effect on the storm. However, over the past six hours, Daniel has increased in strength. The 11 AM satellite shot also shows it regaining a more symmetrical form. This may be due to less influence from the upper level trough which is lifting out to the NE and allowing an environment ripe for redevelopment. Thus, the storm is still a very serious threat to Oahu and Kauai. "Daniel has also slowed in forward motion. It should start to pick up forward speed tomorrow once it is past Oahu. A ridge will be building to our north that will accelerate the storm to the WNW Tuesday evening. "The present slower forward movement is good for surf production. Windward Oahu should see a steady increase in surf today, maxing early tomorrow morning as the storm passes, then steadily subsiding Tuesday night. Due to the proximity of our windward shores to the storm, the surf and rip currents will be exceptionally rough, especially if the center of the storm gets close to Oahu. Wave energy should be filling in today to select reefs in the Country which pick up NE to ENE swell. "The local winds for today will continue light and variable, mostly NW, unless the system gets close. If the system stays to our north, we may not see much wind at all. However, the storm is too close for comfort, with potential for extreme winds to 50+ knots if the deep, convective squalls associated with Daniel brush the island. "On Oahu Tuesday morning, we may have west winds but by late Tuesday, moderate Trades will fill back in. On Wednesday, the surf will slowly settle back toward our typical 1-3' windswell. More great reading:
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