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Hurricane Season 2008: Dolphin (formerly 27W) (Western Pacific)
 
Dec. 17, 2008

Dolphin Weakens to a Tropical Storm at Sea

Tropical Storm Dolphin is still frolicking in the open waters of the Western Pacific Ocean, and that's where it's expected to fade away in a couple of days.

Aqua image of Typhoon Dolphin on Dec. 17, 2008> Larger image
Credit: Credit: NASA/Jeff Schmaltz, MODIS Rapid Response Team
According to the Joint Typhoon Warning Center, the organization that forecasts tropical cyclones in that area of the world, Dolphin has now been downgraded from Typhoon to Tropical Storm status. On Wed. Dec. 17, Dolphin's maximum sustained winds were near 60 knots (69 mph). It was moving northeast near 13 knots (15 mph).

At 9:00 Zulu Time (4 a.m. EST) on Dec. 19, Dolphin was located near 19.4 degrees north latitude and 133.1 degrees east longitude. That's about 575 nautical miles west-southwest of the island of Iwo To. The island received its name on Sept. 1, 2007. On that date, Japan re-named the Pacific island of Iwo Jima, site of the famous World War II battle, to its original name of Iwo To. In Japanese, the new name means the same as Iwo Jima or "Sulfur Island."

This natural-color image of Typhoon Dolphin was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on December 16, 2008. The storm had a closed (cloud-filled) eye, and a thick cluster of thunderstorm clouds occupied the northeast quadrant.

NASA's Tropical Rainfall Measuring Mission (TRMM) satellite can measure rainfall from tropical cyclones, and passed over Dolphin. Rain rates in a few cloud bands on the eastern side of Typhoon Dolphin approached 50 millimeters (almost 2 inches) per hour (red) on December 14, 2008.

Light to moderate (blue to green) rain was observed in other parts of the storm. Dolphin was more than a hundred kilometers (62 miles) east of the Philippines and was forecast to turn northeast, away from the islands, in subsequent days.

TRMM image of Dolphin on Dec. 17, 2008> Larger image
Credit: NASA/Hal Pierce
TRMM was launched in November 1997 with the primary mission of measuring rainfall from space using both passive sensors (sensors that simply measure reflected light or heat) and radar. In this image, rain rates in the center of the swath are from the TRMM Precipitation Radar, while those in the outer swath are from the TRMM Microwave Imager. The rain rates are overlaid on infrared data of clouds from the TRMM Visible Infrared Scanner. The data are overlaid on the NASA Blue Marble. TRMM is a joint mission between NASA and the Japanese space agency, JAXA.

The Joint Typhoon Warning Center forecasts Dolphin to track east-northeast and begin weakening, as wind shear increases (winds blowing at different levels of the atmosphere that tear a storm apart). Dolphin is expected to fade by the weekend.

Text Credit: Rob Gutro, Rebecca Lindsey/NASA's Goddard Space Flight Center


Dec. 15, 2008

Category 2 Typhoon Dolphin Now Heading into North Philippine Sea

AIRS image of Typhoon Dolphin> Larger image
Credit: Credit: NASA JPL
The Dolphin know as Typhoon Dolphin is going to give the Philippines a welcome early Christmas present – it's not going to make landfall there. Instead, the storm is now veering toward the north and staying in the open waters of the Philippine Sea where it is expected to dissipate by Dec. 18.

Typhoon Dolphin, also known as Typhoon 27w, was packing sustained winds near 90 knots (103 mph) and higher gusts on Dec. 15. That makes Dolphin a Category 2 Typhoon on the Saffir-Simpson scale, where that category of storm has sustained winds between 96-110 mph. At 12:00 Zulu Time (7:00 a.m. EST) Dolphin was frolicking in the sea near 15.1 degrees north latitude and 130.4 degrees east longitude. That puts Dolphin's center about 710 nautical miles south-southeast of Kadena, Okinawa, Japan. Dolphin has been moving north near 5 knots (6 mph).

According to the Joint Typhoon Warning Center, the organization that forecasts tropical cyclones in that area of the world, "Dolphin has intensified slightly as convective banding around the low level circulation center deepened as evidenced by the colder tops on infrared satellite imagery." The infrared imagery of the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite is one of those used to identify the cloud temperatures.

When cloud temperatures get colder, it means that clouds are getting higher. Building clouds indicate a lot of "uplift" in the atmosphere and stronger thunderstorms.

The infrared image, taken on Dec. 13 at 11:53 p.m. EST (Dec. 14 at 4:53 UTC) shows a large temperature difference between the tops of the clouds in a tropical cyclone and the warm ocean waters that power it. The lowest temperatures (in purple) are associated with high, cold cloud tops that make up the top of Dolphin. Those temperatures are as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). The blue areas are around 240 degrees Kelvin, or minus 27F.

AIRS infrared signal doesn't penetrate through clouds, so where there are clear skies AIRS reads the infrared (heat) signal from the ocean and land surfaces, revealing warmer temperatures (colored in orange and red). The orange temperatures are 80F (300 degrees Kelvin) or greater (the darker they are, the warmer they are). Tropical cyclones need sea surface temperatures of 80F to strengthen and maintain their strength.

Typhoon Dolphin will move more toward the northwest and will gradually weaken as it drifts into a surge of cool dry northeast monsoon winds extending all the way into the Philippine Sea. By Thursday, Dec. 18, Dolphin is expected to dissipate over the northern Philippine Sea as wind shear increases.

Text Credit: Rob Gutro (from JTWC reports)/NASA's Goddard Space Flight Center


Dec. 12, 2008

Tropical Cyclone 27W Now a "Dolphin" Playing in Open Western Pacific Waters

AIRS image of Tropical Cyclone 27W Credit: NASA JPL/ Ed Olsen
> Larger image
Tropical Cyclone 27W has been given the name Dolphin, now that its reached tropical storm strength in the open waters of the Western Pacific Ocean. Tropical Storm Dolphin was 290 nautical miles north-northeast of Yap. Yap is an island in the Caroline Islands of the western Pacific Ocean. It is a state of the Federated States of Micronesia.

On Dec. 12 at 12:00 Zulu Time (7 a.m. EST), Tropical Storm Dolphin had sustained winds near 40 knots (46 mph), and was located near 14.1 north and 139.2 east. It was moving west-northwestward near 10 knots (11 mph) the Joint Typhoon Warning Center reported. It will continue on a westward track over the weekend of Dec. 13-14 on its way toward the Philippines sometime during the week of Dec. 15.

NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured Tropical Storm Dolphin's cloud temperatures as it romped in the open waters. AIRS produced this infrared image on Dec. 11 at 10:29 p.m. EST (Dec. 12 at 3:29 UTC).

The infrared image shows the frigid cloud top temperatures, giving forecasters a clue to the storm's strength. The coldest temperatures (and highest cloud tops) shown in purple are as cold as 220 degrees Kelvin or minus 63 degrees Fahrenheit (F) or colder. The lower clouds are depicted as the blue areas, which are around 240 degrees Kelvin, or minus 27F.

Text Credit: Rob Gutro/NASA's Goddard Space Flight Center


Dec. 10, 2008

Tropical Depression 27W Forms in Western Pacific Ocean

AIRS image of Tropical Depression 27W> Larger image
Credit: NASA JPL/ Ed Olsen
The twenty-seventh tropical depression has formed in the Western Pacific Ocean. Tropical Depression 27W was 360 nautical miles east of Guam on Dec. 10 and moving westward at 13 knots (14 mph). It is on a westward path to the Philippines by mid-week next week.

On Dec. 10 at 15:00 Zulu Time (10 a.m. EST), 27W had sustained winds near 25 knots (28 mph), and was located near 12.4 north and 150.1 east. It was moving westward. Wind imagery from NASA's QuikScat satellite indicated that the low level circulation center "has begun to rapidly consolidate with 25 knot (28 mph) winds beginning to wrap into the center on the southern periphery of the storm with stronger winds on the northern side of the system," the Joint Typhoon Warning Center reported.

NASA's Aqua Satellite Sees Depression 27W NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite captured 27W's cloud temperatures as it is beginning to get organized. Looking at this image, the round circulation isn't even apparent yet. AIRS produced this infrared image on Dec. 9 at 10:41 p.m. EST (Dec. 10 at 3:41 UTC).

The infrared image shows the frigid cloud top temperatures, giving forecasters a clue to the storm's strength. The coldest temperatures (and highest cloud tops) are normally shown in purple, but the clouds aren't that high yet, as the storm is still weak and getting organized. Purple colored areas are as cold as 220 degrees Kelvin or minus 63 degrees Fahrenheit (F) or colder. Currently, the entire system consists of lower clouds depicted as the blue areas. Those areas are around 240 degrees Kelvin, or minus 27F.

Text Credit: Rob Gutro/NASA's Goddard Space Flight Center