NASA's Aqua satellite passed over newborn Tropical Depression 4C in the Central Pacific Ocean on August 21. TD 4C lies just three degrees east of the International Date Line.
The International Date Line sits on the 180 degree line of longitude in the middle of the Pacific Ocean. When Tropical Depression 4C formed on August 20 at 11 p.m. EDT, it developed near 15.2 North latitude and 177.5 degrees West longitude.
On Aug. 21 at 1340 UTC (9:40 a.m. EDT), NASA's Aqua satellite captured Tropical Depression 4C in infrared light. Infrared data was gathered by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The infrared data showed the coldest cloud top temperatures persisting mostly to the north of the low-level circulation center.
The CPHC noted that recent satellite animations and microwave data show some indications that dry air in the mid-levels may be affecting the southern side of the circulation. Dry air saps evaporation and thunderstorm development.
By 11 a.m. EDT (5 a.m. HST/1500 UTC) on August 21, TD4C's maximum sustained winds were near 35 mpg (55 kph). It was about 515 miles (825 km) west of Johnston Island and 850 miles (1,365 km) south of Midway Island. It was moving to the north at 5 mph (7 kph) and is expected to curve to the northwest by August 22. Minimum central pressure was 1003 millibars.
The CPHC expects TD4 to become a tropical storm late on August 21 or on August 22 as it moves in a northerly direction almost paralleling the International Date Line before turning northeast toward Midway Island by August 26.