Supertyphoon Paka Hits Guam

Supertyphoon Paka hit Guam (and the nearby island of Rota) on December 16, 1997 with sustained winds of 145-150 mph and gusts to near 185 mph. The storm caused an estimated 200 million dollars of damage. Here is a collection of images showing the typhoon near Guam and some of the ways meteorologists look at typhoons and hurricanes.

0632Z GMS-5 Vis (317K JPG)	0732Z GMS-5 IR (170K JPG)
0721Z WSR-88D Reflectivity (221K GIF)	0712Z WSR-88D Base Velocity (152K GIF)

The upper left hand image (317K JPG) is a visible image from the Japanese GMS-5 geostationary satellite taken at 0632 UTC December 16. This satellite orbits over the Equator 22,300 miles above the Earth's surface, so it stays in one place relative to the Earth. The satellite makes images in several different channels, including reflected visible light. At this time, the cloud-filled eye is just northeast of Guam. Bands of showers and thunderstorms are coiled around the eye. Filmy clouds are seen further away from the eye, especially to the west and south. These are high cirrus clouds associated with the typhoon's upper level outflow. A healthy typhoon like Paka has an upper level high over it, which means in the Northern Hemisphere its outflow clouds are rotating clockwise while the thunderstorms are rotating counterclockwise. (This image is courtesy of the Naval Research Laboratory Tropical Cyclone page.)

The upper right hand image (170K JPG) is an infrared image from the GMS-5 at 0732 UTC December 16, 1997. Notice the color scheme of this image (given in the color bar at the bottom). The satellite's infrared scanner is reading the temperature of the surface beneath, whether that is the ground, the ocean, or clouds. This color scheme enhances the colder (taller) clouds associated with the typhoon. It is used by tropical cyclone warning centers to estimate tropical cyclone intensity. Notice the area of black with the two curved white bands. The eye is a warm spot (lower clouds) inside the inner curved band (the eyewall). The outer curved band suggests that concentric eyewalls were present, which is usually only seen in intense tropical cyclones. At this time, Paka (which was moving about 7 mph) is still just northeast of Guam. (This image is also courtesy of the Naval Research Laboratory Tropical Cyclone page.)

The lower left hand image (221K GIF) is a radar reflectivity image from the WSR-88D on Guam. The image is colored according to the intensity of the rainfall in Paka, with the color scale to the right. The most prominent feature is the closed ring of gold and red which is over northern Guam (on the southwest side) and Rota (on the north side). This is the outer eyewall of Paka. The broken ring on the inside is the inner eyewall, which is open to the northeast. The radar is sampling the eyewalls at low levels in the storm, while the satellite is seeing only the cloud tops. Thus, the radar gives a better depiction of the concentric eyewalls. (This image is courtesy of the Joint Typhoon Warning Center.)

The lower right hand image (152K GIF) is a base velocity image from the Guam WSR-88D. The Doppler radar can detect the velocity of the wind component blowing directly toward or directly away from the radar. In this image, the velocities blowing toward the radar are in shades of blue, black, and green, while the veolcities blowing away from the radar are in yellow and red. (The scale is again to the right.) Since Paka's winds are blowing counter-clockwise around the eye (located northeast of Guam), the strongest winds blowing toward the radar (138 kt) are in the dark blue area west of the eye and north of Guam, while the strongest winds blowing away from the radar (124 kt) are in the pale red area south of the eye and east of Guam. The purple areas? That's where the radar can't determine a velocity for one reason or another. It's called range folding, or more informally "purple haze"! (This image is also courtesy of the Joint Typhoon Warning Center.)

1035Z DMSP IR (283K GIF)	1035Z DMSP SSM/I (118K JPG)

About the time Paka passed just north of Guam (1035 UTC December 16), a Defense Meteorological Satellite Program (DMSP) polar-orbiting satellite passed over the area. In contrast to the geostationary satellites, the polar-orbiting satellites fly at a low altitude (typically 600-900 miles above the Earth) and only pass over a given spot twice a day. This means they can make higher resolution images in exchange for less frequent coverage. They also carry an instrument not used on geostationary satellites - the Special Sensor Microwave/Imager (SSM/I). This instrument can see through ice clouds to the water clouds or ocean surface that lies below. Thus, it can reveal details that regular visible and infrared imagery can't see.

The left hand image (283K GIF) is an infrared image. The eye appears as a dark spot in the center of the cloud mass. Notice there is a tightly curved white (tall) cloud band near the eye, with a grayer area separating it from the taller clouds further away. The inner band is the inner eyewall, while the gray area is the moat between the inner and outer eyewalls seen in the radar reflectivity image (221K GIF).

The right hand image (118K JPG) is an SSM/I image in the 85 Ghz channel. In this image, the colder temperatures (shown in yellow, orange, and red on the scale at the bottom) are areas of heavier rainfall. The most obvious feature is the ring of yellow with the embedded red stripe on the southwest side. This is Paka's outer eyewall. The inner eyewall is not apparent in this image, in contrast to the infrared image. This image suggests the outer eyewall is becoming the dominant feature in the typhoon. (The left hand image is courtesy of the Joint Typhoon Warning Center, while the right hand image is courtesy of the Naval Research Laboratory Tropical Cyclone page.)

December 17 1025Z GMS IR (179K JPG)

Images over the next 24 hours indicate that's exactly what happened. Contrast this infrared imaged from 1025Z December 17 (179K JPG) with the infrared image from 27 hours before shown above. Two things stand out. First, Paka's eye is now warmer and much better defined. Second, the cloud tops surrounding the eye are now color-coded cold medium gray and cold dark gray instead of the black and white in the earlier image. This means they are colder and taller. Paka has strengthened and its maximum sustained winds have increased to 185 mph. As badly as Guam was hit, it could have been worse seeing how strong Paka was 24 hours later! (This image is also courtesy of the Naval Research Laboratory Tropical Cyclone page.)

More information on Paka is available in the Synopsis of Supertyphoon Paka at the Joint Typhoon Warning Center.

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