Hurricane Season 2011: Tropical Storm Zaka (South Pacific Ocean)

Two NASA Satellites Eyeing Cyclone Zaka's Path Near New Zealand

Tropical Cyclone Zaka developed over the weekend and has become a tropical storm. Two NASA satellites have been providing temperature and rainfall data on Zaka as it nears Raoul Island and is expected to track near northeastern New Zealand.

Raoul Island or Sunday Island is located in the South Pacific Ocean. It is anvil-shaped and the largest and northernmost of the main Kermadec Islands. It's located about 680 miles (1,100 km) north-northeast of New Zealand's North Island.

NASA's Tropical Rainfall Measuring Mission (TRMM) satellite flew over Zaka from space and captured an image of Tropical Storm Zaka's rainfall on Feb. 6 at 1558 UTC (10:58 a.m. EST). At that time, the heaviest rainfall was occurring south and southwest of the center, falling at more than 2 inches (50 mm) per hour. Light to moderate rainfall between .78 inches and 1.57 inches (20-40 mm) per hour was occurring from the south-southeast to the northeastern quadrants of the storm.

TRMM is a joint mission between NASA and the Japanese space agency JAXA that can estimate rainfall in a tropical cyclone from its vantage point in space.

When NASA's Aqua satellite passed over Tropical Storm Zaka on Feb. at 02:05 UTC (10:05 p.m. EST on Feb. 6), the Atmospheric Infrared Sounder (AIRS) instrument took the temperatures of the system's thunderstorm cloud-tops. A large area of strong thunderstorms with heavy rainfall surrounded the center and their cloud tops were as cold as or colder than -63F/-52C. Satellite imagery also shows that Zaka has a well-defined center of circulation, and convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) and thunderstorms are wrapping around the storm's eastern side. That banding of thunderstorms to the east of the storm's center were visible in the TRMM imagery.

The reason for more thunderstorms and convection on the east side of the storm is an upper-level low pressure area sitting to the northwest of the storm. That upper-level low is suppressing convection on the western side of Zaka.

New Zealand’s Metservice expects Tropical Storm Zaka to bring thunderstorms, gusty winds, rough surf and the heavy rainfall that both NASA's Aqua and TRMM satellites noticed to Raoul Island as it passes between 90 and 120 miles (~150 to 200 km) west of the island this evening (New Zealand local time).

Zaka had maximum sustained winds near 40 mph (64 kmh/35 knots) at 0900 UTC (4 a.m. EST) today, Feb. 7. It was still 550 miles northeast of Auckland, New Zealand, near 29.3 South and 179.3 West. It was moving south-southwest near 25 mph (40 kmh/22 knots) and kicking up waves 14 feet (4.2 meters) high.

Because Zaka is moving into an area with increased wind shear (winds that can weaken and tear a storm apart) it is expected to weaken as it passes northeast of New Zealand's North Island tomorrow.

Text Credit: Rob Gutro, NASA's Goddard Space Flight Center, Greenbelt, Md.
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