Cyclone Pam Threatens Vanuatu, Strengthens to Category 5 in South Pacific

Jon Erdman
Published: March 12,2015


 

Tropical Cyclone Pam reached Category 5 strength late Friday morning, local time, in the South Pacific Ocean as it nears its closest pass to the island chain of Vanuatu.

Cyclone Pam Infrared Satellite Image

On Friday afternoon local time (15 hours ahead of U.S. Eastern Daylight Time), Cyclone Pam continued to pack maximum sustained winds estimated at 160 mph, according to the U.S. military's Joint Typhoon Warning Center. The center of Pam was located less than 110 kilometers (70 miles) east of Ambrym, an island in central Vanuatu. Ambrym, in turn is about 100 miles north of the capital, Port Vila.
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.
The center of the cyclone's circulation is expected to impact Port Vila. "[It's] very bad news for Efate (population of 60,000) and the capital of Port Vila - they should at least get into the western eyewall," said The Weather Channel meteorologist Matt Crowther.
Cyclone Pam may yet intensify a bit more thanks to favorable winds aloft flowing outward from the center of circulation, and warm sea-surface temperatures along its path. Some particularly intense convection showing up on infrared satellite imagery Thursday in the northern half of the eyewall suggested further intensification, which indeed eventually occurred.
On the other hand, intense tropical cyclones like Pam typically undergo one or more eyewall replacement cycles, during which a second, outer eyewall forms and contracts inward toward the eye, choking off the old, inner eyewall. During this time, the cyclone's intensity typically weakens a tad. These cycles are not predicted well by forecast models.
Regardless, a track just a bit west of due south is expected to bring the center of Cyclone Pam, or its eyewall, dangerously close to the eastern islands of Vanuatu Friday, local time. The Republic of Vanuatu is an island chain about 1,200 miles northeast of Brisbane, Australia, with a total population of around 224,000.

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

(INTERACTIVE MAP: Vanuatu)
The Vanuatu National Disaster Management Office issued a red alert for the northern half of the island chain, including Torba and Penama Provinces. Yellow alerts were posted for the rest of the island chain, including Sanma, Malampa, Shefa and Tafea Provinces.
According to Vanuatu Meteorological Services, damaging winds, very rough to phenomenal seas, and heavy swells will affect Torba, Penama, Sanma and Malampa provinces. Coastal flooding, flash flooding and landslides are also expected. Winds gusting over 65 mph may reach northern Vanuatu, particularly in outer rainbands shortly.
The most severe impacts from Pam would occur with the closest approach of the eyewall Friday afternoon into Saturday morning, local time, in the central and southern islands of Vanuatu, including Penama, Malampa, Shefa and Tafea provinces.
The Joint Typhoon Warning Center estimates "hurricane-force" winds extend up to 35 miles from the center. Therefore, any deviation of the center further west, i.e. along the western side of the forecast path, would mean a greater danger for those islands.
The capital and largest city in Vanuatu, Port Vila (population around 44,000), is located on the island of Efate in southern Vanuatu's Shefa Province.
(CURRENT CONDITIONS: Santo Island/Pekoa Airport | Port Vila)
Bands of rain triggering local flash flooding, dangerous waves and local coastal storm surge flooding may also affect parts of Fiji, just over 650 miles east of Port Vila.
Pam is then expected to 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.
(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 Marcia Hits Australia (February 2015)