Pacific hurricanes rage over the eastern North Pacific, between Hawaii and the American coast. Most form in warm waters off Mexico and Central America between mid-May and November, with the greatest concentration from July through September.

Until satellite came along in the 1960s, most Pacific hurricanes went undetected in the lightly traveled east-central Pacific. In fact, the number of hurricanes that satellites observed roiling up eastern Pacific waters surprised tropical meteorologists. On average, 18 Pacific tropical storms and 8 hurricanes develop annually, almost twice the Atlantic tally. The numbers are reduced during La Ninas, but increased for El Niños.

Tropical trade winds generally steer these Pacific storms westward into the open ocean, so very few make landfall. Most that do strike Mexico's West Coast, bringing dangerous winds, heavy rain, and threats of flash floods and mudslides.

If a hurricane curls back toward the California coast, the cold California Current, whose waters rarely exceed 60o Fahrenheit, robs the storm of its power and fury. No hurricane has ever hit California, though some tropical storms have.

Every few years, a storm crosses the Pacific to worry Hawaii, but most diminish before reaching the Islands because the nearby waters remain too cool to sustain a hurricane's intensity. Storms surviving the westward journey into "typhoon" waters retain their original designation as a hurricane. This year, the first for predicting Pacific Hurricanes, forecasters are expecting 10 to 15 storms, with up to nine developing into hurricanes.

Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook is funded by Subaru and The National Science Foundation.