Tropical Cyclone 04B formed over the Malacca Strait on Tuesday.  At 10:00 a.m. EST on Tuesday the center of Tropical Cyclone 04B was located at latitude 4.8°N and longitude 98.6°E which put the center about 35 miles (55 km) east-northeast of Langsa, Indonesia.  Tropical Cyclone 04B was moving toward the west-northwest at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 999 mb.

A low pressure system over the Malacca Strait strengthened on Tuesday and the U.S. Joint Typhoon Warning Center designated the system as Tropical Cyclone 04B.  The India Meteorological Department was classifying Tropical Cyclone 04B as a Depression.  It could be the first Tropical Cyclone observed to form over the Malacca Strait in the modern era.

Tropical Cyclone 04B formed in an environment characterized by strong vertical wind shear.  An upper level ridge over the Western North Pacific Ocean was causing strong easterly winds that were blowing toward the top of the tropical cyclone.  Those winds were causing strong vertical wind shear.  The strong winds were causing the distribution of thunderstorms in Tropical Cyclone 04B to be asymmetrical.  Thunderstorms were occurring in bands in the western side of the tropical cyclone.  Bands in the eastern side of Tropical Cyclone 04B consisted primarily of showers and lower clouds.

The circulation around Tropical Cyclone 04B was small.  Winds to tropical storm force extended out 60 miles (95 km) from the center of circulation.

Tropical Cyclone 04B will move through an environment that will be marginally favorable for intensification during the next 12 hours.  Tropical Cyclone 04B will move over water where the Sea Surface Temperatures are near 29°C.  However, the upper level ridge over the Western North Pacific Ocean will continue to cause strong vertical wind shear.  The strong vertical wind shear will seriously inhibit intensification, but the shear may not be enough to prevent some  intensification.  Tropical Cyclone 04B could intensity a little during the next 12 hours.

Tropical Cyclone 04B will move around the southwestern end of a high pressure system that is over the Western North Pacific Ocean and Southeast Asia.  The high pressure system will steer the tropical cyclone toward the west-northwest during the next 24 hours.  On its anticipated track, Tropical Cyclone 04B will make landfall in northern Sumatra near Idi in 12 hours.

Tropical Cyclone 04B will bring strong winds and heavy rain to Aceh province in northern Sumatra.  Heavy rain is likely to cause flash floods in some locations.