Hurricane-to-be Hilda and 'opihi picking: Don't turn your back

Hawaii media cheerily announced this morning that Hurricane-to-be Hilda is unlikely to impact the Hawaiian Islands.

That, of course, is so misleading that it's scary.

(Image: The National Weather Service's Mariner's 1-2-3 rule for Tropical Storm Hilda. Source: NOAA.)

First, the Islands certainly won't avoid pounding hurricane-generated surf on southern shores. Might not be as big as surf from some other hurricanes, but there will be surf.

Second, there is a chance the Islands will feel some wind if the the storm center tracks along the northern edge of its forecast path.

Hurricanes are often depicted as dots on a map, representing the center of the storm.

But these cyclones are major features on the surface of the planet, hundreds of miles wide, spreading swaths of destruction along their paths. And in the Northern Hemisphere (that's us) the winds are stronger and extend farther out on the right side of their path—in the case of Hilda, the northern side.

The National Weather Service's favored estimate has its center passing several hundred miles to the south of the main Hawaiian Islands. If it stays down there, there will be some accuracy to the Star-Bulletin's “at this point it is not expected to have much impact on Hawaii’s weather,” and The Advertiser's “Isles unlikely to feel Hilda's passing.”

The news reports might be right, but would you bet your house on that?

This is a strengthening tropical cyclone, running parallel to the island chain, at this writing about 525 miles from Hilo, and moving at more than 200 miles a day. Right now, tropical storm force winds cover a swath 150 miles wide, and that will increase as it reaches hurricane strength sometime Thursday.

Some sailors—cautious for good reason; their lives and their vessels are at risk—use what's called the Mariner's 1-2-3 Rule. They take the forecast storm center positions and apply a 100-mile circle of possible error at 24 hours out, then 200 miles at 48 hours, and 300 miles at 72 hours. Then they push the circles farther to reflect how far tropical storm force winds extend. Tropical storm winds are 39 miles an hour and more.

If you apply the Mariner's 1-2-3 rule to Hilda, the southern Big Island is within the zone. See the image above.

Media reports unfortunately often shuttle between panic and calming reassurance. The best indications are that Tropical Storm Hilda will remain far enough south to have minimal impacts, but Hawai'i residents need to heed the lesson of 'opihi pickers—go about your business, but don't turn your back to the ocean.

© Jan TenBruggencate 2009