Thursday | November 23, 2017
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THE FORECAST: Experts say Pacific could see busy hurricane season

This past week, a tropical cyclone was spawned in the warm waters off the southwest coast of Mexico. Because it was far out to sea, the mass of churning energy had nothing to destroy.

Harmless though Hurricane Amanda was, the cyclone winds approached category 5, constituting the strongest hurricane on record in the eastern Pacific for the month of May — and also the earliest on record for a category 4. Major hurricanes usually don’t form in the eastern Pacific until June.

The hurricane served as a reminder that weather forecasters will soon be glued to their computer screens, modeling storm tracks and intensity via ocean sensors, satellites and reconnaissance aircraft, and that emergency officials will be keeping an eye on weather patterns in the eastern and central Pacific.

Officials at the Central Pacific Hurricane Center are expecting a busier than normal hurricane season this year because of a developing El Nino cycle in the tropical

Pacific. Scientists predict four to seven tropical cyclones in the Pacific Basin; an average season has four to five. The hurricane season runs from June 1 to Nov. 30 and peaks from July to September.

El Ninos foster hurricanes by reducing the vertical wind shear that normally works to tear cyclones apart as they form. But it isn’t just lower wind shear that could stir the pot during an El Nino year.

“The ocean temperatures are higher, which is conducive to stronger storms,” said Jim Kossin, a climate scientist with the National Climatic Data Center.

Historically, the busiest hurricane years have coincided with the El Nino cycle. The 1992 and 1994 seasons were both El Nino years and both had 11 storms, the most since 1971.

Scientists say Pacific Basin hurricane activity has been in a lull since 1995 and may be entering a cycle of higher activity this year.

Sea temperatures in the Pacific Basin have increased just under one degree Fahrenheit since mid-March, putting the Pacific on course for a low-end El Nino event this year, said Mike Cantin, warning coordination meteorologist for the Central Pacific Hurricane Center.

The current prediction is for the warming to stay around that level, which could increase storms, but likely not to the level of strong El Nino years like 2009, which had sea surface temperature increases around 2.9 degrees. There were seven tropical cyclones in the Central Pacific that year.

“In general, the warmer the water, the stronger the influence,” Cantin said, but noted that an El Nino is tricky to predict.

“It’s hard enough to predict if it will occur, and strength is even harder,” he said.

Researchers are also finding evidence that climate change may increase the frequency and ferocity of tropical cyclones, and put them on a track closer to Hawaii.

A new study shows that hurricanes and typhoons are moving out of the tropics toward both poles — meaning that hurricane paths in the Central Pacific will tend to migrate north toward Hawaii over time. The study, published in the science journal Nature this month, finds that tropical cyclones are reaching maximum strength at higher latitudes each decade. Kossin, a co-author of the study, believes the tropical belt has widened by about 70 miles each decade in the past 30 years and moved the “storm nurseries” where cyclones are spawned. The result is that cyclones in areas around Hawaii peak up to 18 miles farther north each decade.

The migration is occurring only slowly over time, but should be considered in long-range planning, Kossin said in an email.

“If the widening of the tropical belt is mostly caused by greenhouse gases, then (this) will likely continue,” Kossin said. “If it’s caused mostly by atmospheric pollution, and future clean air acts mitigate this, then we may see (it) fade. There is still quite a lot of uncertainty in what the causes are.”

Climate change is expected to not only raise sea levels but also increase the intensity of hurricanes and typhoons. Rising sea surface temperatures will likely elevate the intensity and frequency of such events and make the hurricane season longer in the near future, according to the Intergovernmental Panel on Climate Change.

“Amanda has just broken a record,” Kossin said, “but hopefully this is not a sign of the season to come.”

Email Bret Yager at byager@westhawaiitoday. com.


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