Cyclone Pam Moving Away From Vanuatu

Jon Erdman
Published: March 14, 2015

Cyclone Pam made a direct hit, packing Category 5 winds, on March 13 in the Republic of Vanuatu in the South Pacific Ocean, including the capital city of Port Vila. This will likely be one of the worst natural disasters in the island chain's history.
(MORE: Cyclone Pam Latest News)
The outer bands of Cyclone Pam continue to impact New Caledonia as it moves south-southeast.
Pam will weaken this weekend as it encounters increasing vertical wind shear, which acts to displace the cyclone's convection farther from the center of circulation. However, Pam may still be a rather intense "post-tropical" cyclone north of New Zealand early next week, producing high surf along the coast. New Zealand's MetService has issued severe weather warnings for heavy rain and strong winds for northeastern parts of the North Island for late Sunday into Monday.

Cyclone Pam Infrared Satellite Image

As of Monday morning local time (15 hours ahead of U.S. Eastern Daylight Time), Cyclone Pam continued to pack maximum sustained winds estimated at 130 mph (equivalent to a low end Category 4 hurricane), according to the U.S. military's Joint Typhoon Warning Center. Cyclone Pam continues to move away from Vanuatu and conditions have improved in the southern islands.
At the height of its strength, during the evening to late night hours on March 13 (local time), Cyclone Pam produced winds as high as 165 mph, making it the equivalent of a Category 5 hurricane during its closes approach to the islands. The western edge of the eye of Cyclone Pam scraped the eastern edge of Efate island, including the capital of Vanuatu, Port Vila (population 44,000), at about 11 p.m. Friday night, local time.
One satellite estimate from the University of Wisconsin suggested Pam's central pressure may have been as low as 890 millibars. Another estimate Friday morning, U.S. time had a lower pressure (879 millibars). In general, the lower the central pressure, the stronger the tropical cyclone.
The University of Wisconsin estimate is lower (stronger) than all but two Atlantic hurricanes all-time (Wilma '05: 882 millibars and Gilbert '88: 888 millibars). The all-time lowest pressure measured on the Earth's surface was in Super Typhoon Tip (870 millibars) in October 1979. Without reconnaissance aircraft to provide a direct measurement, we'll never know the actual lowest central pressure of Cyclone Pam.
According to data from Australia's Bureau of Meteorology, Port Vila may have been spared the absolute worst-case scenario. BOM wind data showed a peak gust of 60 mph at 12:51 a.m. Saturday local time (9:51 a.m. EDT Friday in the U.S.). This came about an hour after the pressure bottomed out at 942.1 millibars there.
Water levels peaked about 2 feet above normal tide levels, according to the BOM gauge at Port Vila.

The latest forecast path and intensity of Cyclone Pam from the Joint Typhoon Warning Center.

(INTERACTIVE MAP: Vanuatu)
The Vanuatu National Disaster Management Office had issued a red alert for the entire island chain.
Keeping in mind storm surge impact is also heavily dependent on the size, as well as the intensity of a tropical cyclone, here is a list of typical Category 5 wind impacts:

• Some complete building failures. Small utility buildings blown over or away.
• Severe and extensive window, door damage.
• Complete destruction of mobile homes.
• All shrubs, trees, signs blown down.

(MORE: The World's Most Vulnerable Cities For Natural Disasters)
The Republic of Vanuatu is an island chain about 1,200 miles northeast of Brisbane, Australia, with a total population of around 224,000.
Pam's large circulation had already lead to wave-induced coastal flooding on Vaitupu Island, Tuvalu Thursday, according to storm surge specialist, Dr. Hal Needham (thanks to Weather Underground's Dr. Jeff Masters for passing this along) and The Weather Channel hurricane specialist, Michael Lowry. This was just under 800 miles northeast of the center of Pam at the time.
(MORE: Hurricane Central)

Tracks of nine previous Category 5 cyclones in the southwest Pacific Ocean since 1970, according to the Joint Typhoon Warning Center's best track data. Potential forecast path of Cyclone Pam as of March 11, 2015 is overlaid by faint red shading.
(Michael Lowry/The Weather Channel)

Are Category Fives Unusual There?

In reliable records dating to 1970, there have been nine other Category 5 cyclones in the southwest Pacific Ocean basin, according to hurricane specialist, Michael Lowry. Cyclone Ului was the last to do so in March 2010 well west of Vanuatu in the Coral Sea.
Based on that, one would expect "about one Cat. 5 (cyclone) every five years" in the southwest Pacific basin, says Lowry.
Of course, with no reconnaissance aircraft missions in this part of the world, cyclone intensities are assigned using satellite estimates.
The Atlantic basin has not had a single Category 5 hurricane since Hurricane Felix in early September 2007.
November through April is the season for tropical cyclones in the southwest Pacific Ocean, called simply "cyclones" there, rather than "hurricanes" or "typhoons". Cyclones Lam and Marcia made landfall in northern Australia in mid-late February.

MORE: Cyclone Pam Hits Vanuatu