Scientists Discover Hurricane-Prone Westerly Winds

[Excerpted from DisasterRelief, 24 Apr 2000, Written by Stephanie Kriner]

Before predicting a hurricane in the Gulf of Mexico or the Caribbean Sea, forecasters can start listening for westerly winds blowing in from as far away as Indonesia. Scientists previously had thought that mountains in Central America protected the tropics from these potentially stormy gusts. But a new study has revealed that tropical storms and hurricanes are four times more likely to churn in the waters of the Caribbean or Gulf when Pacific winds blow from the west than from the east.

The scientists from the University of Washington in Seattle (UW) culled data from climate and weather records accumulated between 1949 and 1997. The records revealed that westerly winds that blow during a weather phemonena called the Madden-Julian Oscillation have a strong correlation with hurricane formation.

The oscillation, which shifts wind directions from easterly to westerly, begins in the Indian Ocean about every 30 to 60 days. It moves across the Pacific, hugging the equator until it reaches the Americas, where the chances of a hurricane rise astronomically. It takes about 15 days to impact storm formation in the Gulf or Caribbean, researchers say.

The finding was a startling revelation for scientists who originally thought Pacific winds could have little effect on Atlantic storm formation.

“We were sort of surprised,” said Eric Maloney, a UW doctoral student who completed the study along with Dennis Hartman, a UW atmospheric science professor. The researchers had incorrectly assumed that mountains and high terrain in Central America would block winds from reaching the Caribbean or Gulf.

In fact the researchers still aren't sure how the low-level winds penetrate the mountains. One explanation is that the air seeps through gaps among the peaks, Maloney said. Or it could be due to some unknown phenomena. “Something at the upper levels could be causing wind to change over the Caribbean and Gulf of Mexico,” Maloney said.

Despite the unanswered questions, the finding can help improve weather forecasts, allowing meteorologists to monitor the oscillation’s cycles to predict possible hurricanes.

.... The researchers found that one in three Madden-Julian Oscillations occuring during the hurricane season (between June and November) triggers storm activity in the Gulf or Caribbean. They also discovered that stronger westerly winds result in stronger storms.

Maloney and Hartman aren't sure why the Madden-Julian Oscillation acts as a catalyst for hurricanes, but they have come up with two possibilities. One theory is that westerly winds over the eastern Pacific create counter clockwise rotations to their north. These rotations are usually associated with low-pressure systems which can develop into storms.

Another theory is that low pressure zones that usually form just to the east and north of westerly winds draw air to the center of the oscillation, where it rushes upwards. This wind movement can foster hurricanes and tropical storms, Maloney said.

Previously, Maloney found a strong link between westerlys and the formation of hurricanes in the eastern Pacific. The researchers now are looking at storms that form over the Atlantic Ocean.

“We have come up with no conclusion yet,” Maloney said. “We’re hoping to find out if the Madden-Julian Oscillation affects hurricanes over that region also.”