Hawai'i 2009 highest tides January 10--roll up your trousers

The highest tides of 2009 for Hawai'i are just a week away as this is written, and people near the shore should be alert.

From January 9 to 11, the highest tides, a few hours before dawn, will be 2.6 feet or higher in Honolulu, with the peak on the 10th.

Depending on where you are in Hawai'i, the peak may be a little higher or lower, and a little earlier or later, but generally, folks will see a remarkably high high waterline when they get up on the 10th.

It means, of course, flooding in Mapunapuna, docks under water at Nawiliwili, beaches razor thin or gone entirely, and all the other features associated with the highest water.

What isn't entirely clear is what other factors will be driving that water even higher or lower.

That's because tides operate on top of the regional sea level, that can change due to a number of factors.

During certain climate events, like El Nino periods and strong low pressure systems, the base water level can be higher than normal. Warm water expands and can create regional high sea levels. There are oceanic gyres that can cause vast regions of the ocean to form a kind of hump. High tides atop these can drive water farther inland than normal.

Strong waves atop high tides can also push flooding waters inland.

Chip Fletcher, the coastal geologist at the University of Hawai'i's School of Ocean and Earth Science and Technology, said he's not sure how severe the early January tides will be.

“Any swell that accompanies them will be a problem, but cool water this time of year should ameliorate a bit,” he wrote in an email.

And all these features—tides, gyres, storms and the rest—operate atop the base sea level, which for the last century has been rising.

Sea levels have risen twice as much at Hilo than at Kaua'i and O'ahu. That is explained by the geological phenomenon in which the great weight of the young Big Island is actually pushing down on the Earth's mantle, causing the island to sink. The sinking is over for the severely eroded older islands.

The difference in sea levels ranges from about half a foot of rise on the older islands to a foot on the youngest, over the past century. For graphical views of measured sea level changes at various locations in Hawai'i, see the NOAA Tides & Currents site at http://www.tidesandcurrents.noaa.gov/sltrends/sltrends_states.shtml?region=hi.

The sea level trend seems inescapable, and all indications are that seas will continue to rise, and perhaps faster than before (see previous post at http://raisingislands.blogspot.com/2009/01/sea-level-threat-worsens-will-hawaii.html.)

©2009 Jan TenBruggencate