The low pressure area formerly known as System 92S has strengthened overnight and developed into Tropical Storm Errol today, April 15. Infrared imagery from NASA’s Aqua satellite showed strong thunderstorms near Errol’s center, but they remained off-shore from Western Australia’s northern coast.

An infrared image on April 14 at 0517 UTC from NASA’s Atmospheric Infrared Sounder (AIRS) instrument shows that Tropical Storm Errol’s strongest thunderstorms with the coldest, highest cloud tops were off-shore from the northern coast of Western Australia. Those thunderstorms had cloud-top temperatures as cold as or colder than -63 F/-52C and brought heavy rainfall. Multispectral satellite imagery also showed a well-defined center of circulation in Errol, and bands of thunderstorms wrapping around its souther and western edges.

Errol has sustained winds of 40 knots with higher gusts, and is kicking up rough surf along the northern coast of Western Australia today. Errol’s center was about 270 miles (434 km) west of Darwin, Australia near 13.1 South latitude and 126.3 East longitude. Errol is currently drifting south-southwestward at 2 knots (2 mph/~4 km) but is expected to start moving to the west-northwest as a result of a strengthening ridge of high pressure building up over Western Australia.

Bune is now an extra-tropical cyclone in the Southern Pacific Ocean far to the northeast of northern New Zealand. NASA infrared data is showing weaker thunderstorms and waning convection, indicating that Bune is on its way into history. According to the New Zealand Meteorological Service, extra-tropical Cyclone Bune is expected to stay to the northeast of Gisborne on March 30 and will then move away toward the southeast on March 31. Rains that are forecast for Gisborne on March 30 will be from southerly wind flow and not associated with extra-tropical cyclone Bune.

NASA’s Aqua satellite flew over Bune on Sunday, March 27 when it was still a weak category one cyclone with maximum sustained winds near 74 mph (119 kmh/64 knots). The image still showed that Bune had an eye at that time. Animated satellite infrared imagery today, March 29, taken from the Atmospheric Infrared Sounder (AIRS) instrument that also flies aboard the Aqua satellite showed that the cloud tops of the thunderstorms were warming quickly and convection was dissipating. Warming cloud tops indicate that the thunderstorms are falling in height, and the lower the thunderstorms, the less powerful the uplift behind them is, and the weaker they are.