Typhoon 'Choi-Wan' appears have undergone an eyewall replacement cycle in the past 6 hours or so. The rainband structure continues to develop impressively as the tropical storm force wind field expands significantly in all quadrants and central pressures head south of the border.

As of this writing (and things are changing quickly) Typhoon Choi-Wan has strengthened to 90 Kts. with estimated lowest pressure at 963 mb and falling steadily. Maximum sustained winds are now forecast to reach 125 Knots (145 mph) with gusts as high as 150 Knots (170 mph), ranking it as a Strong Cat 4 'Hurricane' on the Saffir-Simpson Scale of tropical cyclone intensity.

Comparing the following Passive Microwave Image with the one from above reveals just how significantly this cyclone has managed to organize over a relatively short time.

Notice, especially, the much more solid looking eyewall structure and the spiral rainbands that now completely encircle the inner core of the cyclone.

It will be interesting to follow the structure of Choi-Wan, as revealed by passive microwave imaging, over these next few days as this typhoon ramps up to strong Cat 4 or possible Cat 5 intensity.

The Guam Long-Range Doppler Radar shows (as of this hour) the spiral rainbanding in the SW quadrant of 'Choi-Wan' with the eyewall signature passing just outside the very limits of the long range scan.

For those interested in following the progress of 'Choi-Wan' are invited to check out the following links:

Guam Tropical Cyclone Main Page

Animated Color Enhanced Infrared Satellite Imagery

NRL Tropical Cyclone Main Page - Click on 'Choi-Wan' on the left side

Fortunately, Typhoon 'Choi-Wan' will be passing well to the north of Guam and Saipan and will be over open ocean as it attains its peak intensity in a few days and is likely to recurve at a safe distance west of Iwo Jima.