Category 5 Tropical Cyclone Pam Makes a Direct Hit on Vanuatu

The South Pacific island nation of Vanuatu is taking an extreme pounding from the 165 mph winds of Category 5 Tropical Cyclone Pam, one of the strongest tropical cyclones ever recorded in the waters east of Australia. According to microwave satellite images from the Navy Research Lab, the eye of Pam passed directly over several small islands north of the main Vanuatu island of Efate near 4:05 am EDT March 13, making Pam Earth's first landfalling Category 5 tropical cyclone since Super Typhoon Haiyan hit the Philippines in November 2013. Pam is continuing southwards, and its western eyewall passed over the eastern side of Efate Island near 8 am EDT. Efate is the most populated island in Vanuatu, with a population of 66,000, and is home to the capital city of Port Vila. With top sustained winds of 165 mph as of 8 am EDT Friday, as estimated by the Joint Typhoon Warning Center (JTWC), eastern Efate likely experienced severe to extreme damage from Pam, even though the island was on the weaker (left front) side of the eyewall. Fortunately, Port Vila is on the southwest side of the island, and missed the strongest winds of the eyewall. Observations from Port Vila remained online through Pam's closest approach, and a minimum pressure of 942 mb was recorded, with top winds of 31 mph, gusting to 59 mph. A Personal Weather Station in Port Vila had received 4.69" of rain from the storm as of 4 am EDT Friday, before going off-line. The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam bottomed out with a central pressure of 899 mb at 8 am EDT Friday.


Figure 1. Tropical trouble: four tropical cyclones churn the Pacific in the this afternoon VIIRS image from March 12, 2015. Pam is in the right center of the image. Image credit: NOAA Visualization Lab.


Figure 2. Tropical Cyclone Pam approaching Vanuatu's capital city of Port Vila on Efate Island, as seen by the MODIS instrument on the Aqua satellite at 10:20 pm EDT March 12, 2015. At the time, Pam was a Category 5 storm with 160 mph winds. Image credit: NASA.

Satellite loops show that Pam is a huge and fearsome-looking storm, with a prominent 17-mile diameter eye and a very large area of intense eyewall thunderstorms with extremely cold cloud tops. These clouds have cold tops due to the fact that the strong updrafts in the eyewall are pushing the cloud tops to the base of the stratosphere. Sea surface temperatures are near 30°C (86°F), which is about 1°C (1.8°F) above average. Warm waters extend to great depth beneath the cyclone, giving Pam a huge amount of heat energy to draw upon. Wind shear Friday morning was low, near 10 knots, and is expected to be low to moderate though Saturday morning, which should allow Pam to remain an extremely dangerous Category 4 or 5 storm. The 8 am EDT Friday official intensity forecast from the Joint Typhoon Warning Center (JTWC) did not forecast any additional intensification of Pam. 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. However, Friday morning microwave satellite images showed no signs that Pam is ready for an eyewall replacement cycle. These cycles are not predictable by current forecast models.


Figure 3. Track of all Category 5 storms in the South Pacific (east of 135°E) since satellite records began in 1970. Pam is one of only ten Category 5 storms ever recorded in the basin since satellite records began in 1970. The strongest tropical cyclones in the Joint Typhoon Warning Center’s records are Zoe (2002/2003) and Monica (2006), which topped out with 180 mph winds (thanks go to Phil Klotzbach of CSU for this stat.) Image credit: Michael Lowry, TWC.

Impacts of Pam
Pam is likely to be one of the most destructive natural disasters in Vanuatu's history. According to EM-DAT, the international disaster database, the previous most expensive disaster in Vanuatu history was Cyclone Eric of 1985, which did $173 million in damage (1985 dollars.) Though it appears the capital of Port Vila avoided the worst of Pam, the east side of Port Vila's Efate Island was not so fortunate. Pam will also pass very close to or over the three small, southernmost islands of Vanuatu on Friday and Saturday. These islands are Erromango (population 2,000), Tanna (pop 29,000) and Aneiytum (pop 900). Even if the islands miss a direct hit by Category 4 - 5 eyewall winds, hurricane-force winds will extend out 35 miles from the center, and likely cause heavy damage to all of these islands. Regardless of Pam's track, its waves will cause major coastal damage; the significant wave height of the storm was 45 feet at 8 am EDT Friday. The NOAA WaveWatch III model predicted significant waves height of up to 50 ft, as documented by storm surge expert Hal Needham in his latest blog post. Storm surge is a major concern, as well as extreme flash flooding from Pam's torrential rains. After passing Vanuatu, Pam is likely to weaken significantly, but the storm may still be capable of bringing tropical storm-force winds to New Zealand on Sunday. High surf causing erosion and coastal damage will be the main threat from Pam to New Zealand, though.

Pam has already caused significant damage to several islands in the Solomon Islands, just to the north of Vanuatu. According to Radio New Zealand International, Tikopia and Anuta Islands bore the full force of the storm, with people injured from falling trees and houses destroyed by strong winds. Tikopia lost 90 percent of its food crops and fruit trees and the water was contaminated, but the weather was still too rough to launch a boat with emergency supplies. All phone lines to Anuta were down and there was no information about how the island had fared.

Bob Henson will have a new post late this afternoon.

Jeff Masters