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Hurricane Season 2011: Roke (Western North Pacific Ocean)
09.23.11
 
September 23, 2011

This rainfall map was created from TRMM satellite data from Sept. 15 to 22, 2011 over and around Japan. › View larger image
This rainfall map was created from TRMM satellite data from Sept. 15 to 22, 2011 over and around Japan. It shows a band of very heavy rain stretching northeastward from eastern Kyushu across Shikoku and into southern Honshu from 300 mm (~12 inches, shown in green) to in excess of 550 mm (~22 inches, shown in red). Rainfall of 50 mm/~2 inches appear in light blue, and over 150 mm (~6 inches are shown in blue. )The thin black line is Roke's track, storm symbols mark Roke's 6-hourly positions.)br /> Credit: SSAI/NASA, Hal Pierce<
NASA's TRMM Satellite Maps Japan's Heavy Rainfall from Typhoon Roke

Typhoon Roke, which made landfall as a Category 1 typhoon along the southeast coast of Honshu near the city of Hamamatsu (about 200 km southwest of Tokyo), was responsible for bringing heavy rains and flooding to most of Japan. A map created by NASA shows the heavy rainfall as measured by the TRMM satellite.

Heavy rains actually began affecting parts of southern Japan well before the cyclone neared the coast as tropical moisture from Roke streamed northward into a stalled out frontal boundary that was draped across southern Japan. Japan is also very mountainous, which can enhance the effect. The Tropical Rainfall Measuring Mission or TRMM satellite is used to measure rainfall from space over the global Tropics using a combination of passive microwave and active radar sensors.

For expanded coverage, TRMM can be used to calibrate rainfall estimates from other satellites. Rainfall estimates from the TRMM-based, near-real time Multi-satellite Precipitation Analysis (TMPA) at the NASA Goddard Space Flight Center, Greenbelt, Md. were compiled for the period from Sept. 15 to 22, 2011 over and around Japan. TMPA rainfall estimates show a band of very heavy rain stretching northeastward from eastern Kyushu across Shikoku and into southern Honshu.

Rainfall amounts within this band range from 300 mm (~12 inches) to in excess of 550 mm (~22 inches). Rainfall amounts along the actual track of Roke (shown by the thin black line), though significant, are substantially less, and generally range from 50 mm (~2 inches) to over 150 mm (~6 inches) with occasional higher amounts. The reason for the lighter amounts with the actual passage of Roke was that the storm accelerated as it neared the coast and moved quickly across Honshu before heading back out to sea. So far, 16 people have been reported dead or missing as a result of the storm.

TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Text credit: Steve Lang,
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.



TRMM image of Typhoon Roke ›View larger image
TRMM revealed that Roke was becoming less organized as it approached Japan. Most of the rain, which is mainly moderate - between .78 to 1.57 inches (20 to 40 mm) per hour (shown in green), is located on the east side of the storm with very little on the southwest side. The center is still fairly well defined but is no longer closed with a break in the eyewall evident to the southwest (note the incomplete ring of rainfall near the middle).
Credit: SSAI/NASA, Hal Pierce
TRMM Satellite Analyzes Rainfall as Typhoon Roke Makes Landfall In Central Japan

Roke, a once powerful Category 4 typhoon with sustained winds estimated at 115 knots (~132 mph), came ashore in central Japan Wednesday, Sept. 21, 2011 around 2 p.m. local time near Hamamatsu on the southeast coast of Honshu (about 200 km southwest of Tokyo) as a Category 1 typhoon.

Roke began as a tropical depression ten days ago in the central Philippine Sea about 850 miles (~1370 km) south of Japan. For over a week, the cyclone meandered south of Japan with little change in intensity. Roke finally began to intensify on the 19th of September when it became a typhoon just east of the Ryukyu Islands and then took aim for central Japan.

Roke continued to intensify as it moved off to the northeast in the direction of Honshu, briefly reaching Category 4 intensity on the 20th, before starting to weaken as it approached the Japanese coast.

With its array of passive microwave and active radar sensors, the Tropical Rainfall Measuring Mission satellite (better known as TRMM) has been a valuable tool for observing tropical cyclones around the globe. TRMM captured an image of Roke as it was nearing the Japanese coast. The image was taken at 17:50 UTC (1:50 p.m. EDT) September 20, 2011 (and 2:50 a.m. September 21, local time) and showed the horizontal pattern of rain intensity within the storm. Rain rates in the center swath are based on the TRMM Precipitation Radar (PR), and those in the outer swath on the TRMM Microwave Imager (TMI). The rain rates are overlaid on visible and infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS).

TRMM revealed that Roke was becoming less organized as it approached Japan. Most of the rain, which is mainly moderate in nature (between .78 to 1.57 inches/20 to 40 mm per hour) is located on the east side of the storm with very little on the southwest side. The center is still fairly well defined but is no longer closed with a break in the eyewall evident to the southwest. In the image, that is evident because of an incomplete ring of rainfall near the middle. In fact, Roke was in the process of weakening as its circulation was becoming disrupted by the effects of vertical wind shear.

So far 13 people have been reported missing or dead as a result of the storm, mostly due to river flooding, and hundreds of thousands are without power. After making landfall, Roke passed west of Tokyo before exiting the coast. Roke is expected to continue to race off to the northeast and remain just off the northeast coast of Hokkaido.

TRMM is a joint mission between NASA and the Japanese space agency JAXA.

Text credit: Steve Lang, SSAI/NASA Goddard Space Flight Center


September 21, 2011

NASA's TRMM Satellite Sees Typhoon Roke Intensify Rapidly Before Landfall in Japan

This large-scale image provides context for the 3D radar data (in gray) by showing the three-day surface rainfall accumulation (rainbow colors) along the track of the storm (gray line).
› View larger image
This large-scale image provides context for the 3D radar data (in gray) by showing the three-day surface rainfall accumulation (rainbow colors) along the track of the storm (gray line). Also shown is the significant rainfall accumulation (over 200 mm or ~8 inches) over the Japanese Island of Kyushu to the north of Typhoon Roke. Credit: NASA/TRMM/Owen Kelley


The Tropical Rainfall Measuring Mission (TRMM) satellite captured rainfall and cloud data from Typhoon Roke as it rapidly intensified before making landfall in Japan earlier today.

Typhoon Roke followed a looping path for five days while maintaining tropical-storm strength prior to intensifying to typhoon-strength at 12 UTC (8 a.m. EDT) on September 19, 2011.

When the TRMM satellite flew over Typhoon Roke, it was in the process of rapidly intensifying from a Category 1 to 3 storm on the Saffir-Simpson scale (that measures hurricane/typhoon intensity). Owen Kelley of the TRMM team at NASA's Goddard Space Flight Center in Greenbelt, Md. created a large-scale image that provides context for 3-D radar data by showing the three-day surface rainfall accumulation along the track of the storm. The image also showed significant rainfall accumulation (over 200 mm or ~8 inches) over the Japanese Island of Kyushu to the north of Typhoon Roke.

This rain system continued to interact with Typhoon Roke in the subsequent 24 hours as Typhoon Roke continued moving north toward Japan's largest Island, Honshu.

This image zooms into the inner core of Typhoon Roke during a period of rapid intensification, seen by the TRMM satellite at 1351 UTC (9:51 a.m. EDT) on September 19, 2011.
› View larger image
This image zooms into the inner core of Typhoon Roke during a period of rapid intensification, seen by the TRMM satellite at 1351 UTC (9:51 a.m. EDT) on September 19, 2011. The background is the cloud-top temperatures (seen by TRMM infrared instrument). Dark gray indicates regions where This image shows shallow clouds (dark gray), clouds above freezing level (blue) and clouds that approach the tropopause (light-gray) indicating vigorous convection. Green tinting indicates precipitation reaching an altitude of 8.5 km and yellow tinting indicates an altitude of 11 km. Credit: NASA/TRMM/Owen Kelley


The second image Kelley created zooms into the inner core of Typhoon Roke during a period of rapid intensification, seen by the TRMM satellite at 1351 UTC (9:51 a.m. EDT) on September 19, 2011.

That image showed cloud-top temperatures seen by the infrared instrument on the TRMM satellite and revealed where clouds were shallow, where they reach above the freezing level, and powerful thunderstorms that approached the tropopause indicating vigorous convection (rapidly rising air that form thunderstorms that power a tropical cyclone).

By creating an image in 3-D precipitation, becomes visible in the storm clouds. The 3-D image depicted rainfall and cloud height. The 3-D image was color coded where green tinting indicated precipitation reaching an altitude of 8.5 km (5.2 miles) and yellow tinting indicates an altitude of 11 km (6.8 miles). These altitudes are far above the freezing level that is typically near 5 km (3.1 miles) altitude in the tropics. When air rises more than a kilometer or so the freezing level, any moisture that condenses is likely to form ice hydrometeors instead of liquid hydrometeors and thereby release additional latent heat that may help fuel the storm.

This particular overflight of Typhoon Roke showed a remarkably well-organized circular eyewall especially for a typhoon that was classified at merely tropical-storm strength earlier the same day. However, other aspects of the TRMM radar data suggest modest intensity. Specifically, there is almost no radar reflectivity above 45 dBZ, and the inner volume of >42 dBZ is very small in the circular eyewall. A larger volume of strong reflectivity would indicate the formation of large ice hydrometeors or extremely heavy liquid precipitation. Either event would be evidence of very vigorous updrafts. Also, there was a complete absence of lightning flashes in either the eyewall or in the rainband to the east of the eyewall, based on observations by the TRMM Lightning Imaging System (LIS).

TRMM is managed by both NASA and the Japanese Space Agency, JAXA.

This visible image of powerful Typhoon Roke was captured by the MODIS instrument on NASA's Aqua satellite at 03:55 UTC on Sept. 21, 2011
› View larger image
This visible image of powerful Typhoon Roke was captured by the MODIS instrument on NASA's Aqua satellite at 03:55 UTC on Sept. 21, 2011 as it was approaching landfall in Japan, south of Tokyo. Credit: NASA Goddard MODIS Rapid Response Team


By 11:18 a.m. EDT (15:18 UTC) on Sept. 21, the southern edge of Roke was passing over Tokyo, while the northern extent stretched past Sapporo far to the north.

The Japan Meteorological Agency reported sustained winds of 103 mph (167 kph) and heavy rainfall in Japan's Tokai and Kanto regions earlier today. News reports have attributed four deaths to the storm and noted that rainfall had occurred at 2 inches (50 millimeters) per hour, confirming the data from the TRMM satellite. Roke is expected to re-emerge over water and transition into an extra-tropical storm later today.

Owen Kelley, NASA TRMM Team
NASA Goddard Space Flight Center, Greenbelt, Md.



September 20, 2011

NASA's Aqua Satellite Provides a Visible an Infrared Look at Typhoon Roke

Typhoon Roke captured by MODIS on Sept. 20 at 04:45 UTC (12:20 a.m. EDT).

This visible image of Typhoon Roke was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that flies aboard NASA's Aqua satellite. It was taken on Sept. 20 at 04:45 UTC (12:20 a.m. EDT). Typhoon Roke is a Category Four Typhoon on the Saffir-Simpson scale with maximum sustained winds near 115 knots (132 mph/213 kmh). It was centered 450 nautical miles (833 km/517 miles) southwest of Tokyo but its cloud cover and rains extend over the southern part of the big island of Japan. Credit: NASA Goddard MODIS Rapid Response Team


Typhoon Roke captured on this infrared image from AIRS on Sept. 20 at 0441 UTC (12:41 a.m. EDT).

Typhoon Roke's powerful, high thunderstorm cloud tops were captured on this infrared image from NASA's AIRS instrument on Sept. 20 at 0441 UTC (12:41 a.m. EDT). AIRS flies on NASA's Aqua satellite. This image shows most of the strongest thunderstorms (purple) around the center of circulation. The purple indicates cloud top temperatures colder than -63F (-52C) indicating high, powerful thunderstorms with heavy rainfall. Roke's eye is clearly visible and the storm's northern edge is bringing heavy rains to Japan. Credit: NASA JPL, Ed Olsen



This 3-D image created from TRMM shows convective storm towers near Typhoon Roke's center of circulation › View larger image
This 3-D image created from the TRMM satellite's data shows convective storm towers near Typhoon Roke's center of circulation reached to heights of almost 15 km (~9.3 miles). Red indicates heavy rainfall (2 inches/50 mm per hour).
Credit: SSAI/NASA, Hal Pierce
TRMM saw heavy rainfall in the north and eastern quadrants of Typhoon Roke on Sept. 19, 2011 at 1351 UTC. › View larger image
TRMM saw heavy rainfall in the north and eastern quadrants of Typhoon Roke on Sept. 19, 2011 at 1351 UTC. Red areas are heavy rainfall at 2 inches (50 mm) per hour. Yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour. TRMM also found some towering thunderstorms as high as 15 km (~9.3 miles) high.
Credit: SSAI/NASA, Hal Pierce
NASA Sees Heavy Rainfall in Typhoon Roke - Evacuations Urged in Japan

NASA's Tropical Rainfall Measuring Mission satellite is providing forecasters with a look at the intense rainfall within Typhoon Roke as it continues to near the big island of Japan. TRMM has seen areas with the typhoon where rain is falling at 2 inches/50 mm per hour, and headed to areas of Japan already soaked since last week.

Japanese authorities are calling for evacuations as Typhoon Roke nears because of flooding concerns. According to the Australian Broadcasting Corporation, about 1.1 million people in Nagoya in central Japan's Aichi prefecture were told to evacuate, and other cities in western Japan were given the same request. Heavy rains already occurring in Aichi on Sept. 20 were causing rivers to overflow, according to NHK news. Flash flooding and landslides are of particular concern, especially in the city of Nagoya.

The Tropical Rainfall Measuring Mission (TRMM) satellite passed over Typhoon Roke on September 18 at 1840 UTC (2:40 p.m. EDT). TRMM Precipitation Radar (PR) data showed that Roke contained several areas of heavy rainfall on the eastern side near the center of the storm. Some powerful storms near Roke's center were dropping rainfall at a rate greater than 50mm/hr (~2 inches). TRMM's Microwave Imager (TMI) also revealed that there was a large rain band between Roke and the main islands of Japan. TRMM shows that this large area of rainfall contained smaller lines of intense convective storms.

Tropical storm Roke already had a well defined circulation on September 18 at 1940 UTC (3:40 p.m. EDT) and when the TRMM satellite passed over Roke again on Sept. 19 at 1351 UTC (9:51 a.m. EDT) it had strengthened into a typhoon. TRMM captured the rainfall rates within Roke at that time. The infrared image was created at NASA's Goddard Space Flight Center in Greenbelt, Md. It was created using TRMM's Visible and InfraRed Scanner (VIRS) instrument overlaid with rainfall derived from TRMM PR and TMI data and showed that Roke had a well defined eye, circled by intense bands of rainfall.

A 3-D image of Roke was also created from TRMM data that showed the heights of the towering clouds near Roke's eyewall using data from TRMM Precipitation Radar (PR). Some powerful storms in Roke's eye wall reached to heights of almost 15 km (~9.3 miles). Roke's eye is about 15 miles in diameter and heavy rainfall surrounds it.

Japan's NHK news reported heavy rainfall already in parts of the Miyazaki Prefecture in Kyushu, where 400 millimeters (15.75 inches) had already fallen in one day and over 1,000 millimeters (39 inches) had fallen since last Thursday, so the ground is already saturated.

On Sept. 20 at 8 a.m. EDT Typhoon Roke's maximum sustained winds were near 115 knots (132 mph/213 kmh). It was centered 450 nautical miles (833 km/517 miles) southwest of Tokyo but its cloud cover and rains extend over the southern part of the big island of Japan. It was moving to the northeast at 14 knots (16 mph/26 kmh) and generating rough seas with heights to 26 feet (8 meters).

Roke is picking up speed and is expected to make landfall on Wednesday south of Tokyo while continuing to track to the northeast.

Text credit: Hal Pierce/Rob Gutro,
SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.



September 19, 2011

This infrared image from AIRS shows Tropical Storm Roke (left) and Tropical Storm Sonca (right). › View larger image
This infrared image from the AIRS instrument on NASA's Aqua satellite from Sept. 19 at 12 a.m. EDT, shows Tropical Storm Roke (left) about 630 miles southwest of Yokosuka, Japan, and Tropical Storm Sonca (right) about 395 miles ESE of Misawa, Japan. The purple areas are as cold as -62F/-52 C and are where the strongest thunderstorms and heaviest precipitation is occurring.
Credit: NASA/JPL, Ed Olsen
This visible image from the AIRS instrument shows Tropical Storm Roke (left) and Tropical Storm Sonca (right) › View larger image
This visible image from the AIRS instrument of Tropical Storm Roke (left) and Tropical Storm Sonca (right) shows that the cloud cover extends further than what is seen on infrared, as infrared reveals the highest, coldest cloud heights.
Credit: NASA/JPL, Ed Olsen
This image of Typhoon Sonca was captured on Sept. 18 at 03:20 UTC (Sept. 17 at 11:20 p.m. EDT) › View larger image
This image of Typhoon Sonca was captured on Sept. 18 at 03:20 UTC (Sept. 17 at 11:20 p.m. EDT) as it was making its way past Japan in the western North Pacific Ocean.
Credit: NASA Goddard MODIS Rapid Response Team
NASA Satellite Sees Two Tropical Systems Near Japan

NASA's Aqua satellite captured infrared and visible images of two tropical cyclones near Japan today. Typhoon Roke is near extreme southeastern Japan, while Typhoon Sonca is near east central Japan. Roke is expected to make landfall, while Sonca is not.

NASA infrared images and the visible images tell different stories. The infrared imagery taken from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite takes cloud temperatures, which tell a lot about the system. The colder the cloud top temperature, the higher and stronger the thunderstorms within the storm. That means more uplift or energy in the storm. Wherever the coldest, highest cloud tops are, that's where the heaviest rains are likely falling.

In Roke, AIRS infrared imagery showed a large area concentrated around the storm's center. Infrared satellite imagery also showed deepening convective (thunderstorm) bands wrapping into a ragged eye. In Sonca, the area of strongest thunderstorms was not as large when AIRS captured an image on Sept. 19 at 12 midnight (EDT). That suggests that Roke has more power than Sonca. In addition, convection on Sonca's northern edge appears to be weakening.

The visible images help show that the cloud shield for these tropical cyclones extend further than the infrared images show. That's because the fringes of the storms may have lower, less powerful thunderstorms.

At 11 a.m. EDT on Sept. 19, Typhoon Roke had maximum sustained winds near 70 knots (80 mph/129 kmh). Those typhoon-strength winds extended 20 miles (32 km) from the center, while tropical-storm force winds extend out 110 miles from the center. So, the strongest winds were only about 40 miles (64 km) in diameter. Roke is about 220 miles (354 km) in diameter. Roke was located about 635 miles(1022 km) southwest of Yokosuka, Japan near 28.3 North and 130.4 East. The storm surge with Roke is expected to be strong as Roke is currently generating 26-foot high waves in the western North Pacific Ocean.

Stars and Stripes.com reported that at 4:30 p.m. local time in Japan on Monday, Sept. 19, Tropical Cyclone Condition of Readiness 3 was set for Yokosuka Naval Base at 4:04 p.m. and at 6 p.m. local time for the Naval Air Facility Atsugi. Roke's winds are expected to start affecting Yokosuka on Tuesday. Kyushu is under a tropical cyclone warning. Kyushu is the third largest island of Japan and southwest of Japan's four main islands. Warnings and watches can be found on the Japan Meteorological Agency's web page: http://www.jma.go.jp/en/warn/.

Roke is expected to move northeast and is currently forecast to make landfall near Kyoto and track inland. It will begin to weaken because of vertical wind shear and then move back out into cooler water in the western North Pacific by 1200 UTC (8 a.m. EDT) on Sept. 21.

Typhoon Sonca is about 395 miles (635 km) east-southeast of Misawa, Japan near 27.5 North and 148.8 East. Sonca's maximum sustained winds have increased to 75 knots (86 mph/138 kmh) and the storm is becoming extra-tropical. It is moving to the northeast and away from Japan at 26 knots. Sonca is a compact storm and not as large as Roke. Sonca also has a small, irregular-shaped eye. Infrared imagery showed that convection on the northern edge of the storm is weakening, as cloud temperatures are warmer. Sonca's tropical-storm force winds extend to about 90 miles (144 km) from the center making it about 180 miles (289 km) in diameter. Interestingly enough, the typhoon-force winds cover the same distance as Roke, about 40 miles (64 km) in diameter. Sonca is moving northeast as it undergoes extra-tropical transitioning to the east of Japan.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.



September 16, 2011

This AIRS infrared image was taken on Sept. 15 at 12:295 p.m. EDT. › View larger image
This infrared image was taken on Sept. 15 at 12:295 p.m. EDT and shows the eastern half of Tropical Storm Roke's clouds. The center of Roke is identified by the red hurricane symbol at 26.1 North and 129.6 East. The strongest convection and thunderstorms appear in purple and have cloud temperatures of -63 Fahrenheit, and heavy rainfall.
Credit: NASA/JPL, Ed Olsen
Infrared Satellite Data Shows Tropical Storm Roke Strengthening

Tropical Storm Roke has changed in size and is starting to change in strength. Roke appears to be consolidating in infrared imagery from NASA's Aqua satellite.

Roke began its life as a monsoon depression with a large low-level circulation center that over time consolidated and organized. The eastern half of Tropical Storm Roke was seen in an infrared image from NASA's Aqua satellite AIRS (Atmospheric Infrared Sounder) on Sept. 15, and it showed a more consolidated center with strong convection and very cold cloud-top temperatures.

Cloud-top temperatures are important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the colder the cloud tops and the more powerful the thunderstorms. Cloud top temperatures near Roke's center were near -63 F/-52 C, indicating strong convection.

Infrared imagery also helped forecasters indentify that the center of the storm had recently turned to the southwest.

On Friday, Sept. 16, Tropical Storm Roke had maximum sustained winds near 46 mph (40 knots/74 kmh) and was located approximately 105 nautical miles (120 miles/194 km) east of Kadena Air Base, Japan, near 26.0 North and 129.5 East. Roke was moving slowly to the south-southwest at 2 knots (3 mph). Roke is over 200 miles (321 km) in diameter with tropical-storm-force winds extending out 100 miles (160 km) from the center.

Roke is in a good environment to develop because wind shear (winds that can tear a tropical cyclone apart) remain light and under 5 knots. AIRS infrared data revealed that sea surface temperatures are over the 80F (26.6C) threshold to maintain a tropical cyclone and are in fact as warm as 82F (28C), which will allow Roke to strengthen.

Because there's not much of a steering mechanism to guide Roke , the storm has zig-zagged through the western North Pacific Ocean this week. The Joint Typhoon Warning center noted that there is still no strong steering mechanism, and expects Roke to slowly approach Kadena Air Base over the weekend.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.



September 15, 2011

This infrared image of Tropical Storm Roke was captured on Sept. 14 at 10:41 p.m. EDT.  The purple area indicates the coldest, highest cloud heights, where the heaviest rain was occurring. The orange indicates warm sea surface temperatures over 80F. ›View larger image
This infrared image of Tropical Storm Roke was captured on Sept. 14 at 10:41 p.m. EDT. The purple area around the center of circulation indicates the coldest, highest cloud heights, where the heaviest rain was occurring. The orange indicates warm sea surface temperatures over 80F that are allowing Roke to intensify.
Credit: NASA/JPL, Ed Olsen
Tropical Storm Roke Closing in on Kadena Air Base: Infrared NASA Satellite Imagery

Tropical Storm Roke is showing some signs of intensification on NASA infrared satellite imagery, as areas of strong convection and very cold cloud tops were spotted. Kadena Air Base in Okinawa is now in Roke's sights and should be making preparations.

NASA's Aqua satellite flew over Roke yesterday and the Atmospheric Infrared Sounder (AIRS) instrument showed powerful convection building around the storm's center and over the northern edge. Meanwhile, dry air is wrapping into the low-level center from the southwest, and limiting cloud development.

Infrared imagery provides forecasters with an inside look into the cloud temperatures and heights, and the colder and higher the clouds go, the stronger they become. Meteorologists at the Joint Typhoon Warning Center use infrared imagery to help create their forecasts. AIRS data also showed sea surface temperatures around Roke to be near 27 degrees Celsius (81 Fahrenheit).

On Sept. 15 at 11 a.m. EDT, Tropical Storm Roke was located approximately 175 nautical miles east of Kadena Air Base, Japan, and is moving west at 6 knots (7 mph). Roke is a minimal tropical storm with maximum sustained winds near 35 mph, but expected to strengthen as it closes in on Kadena Air Base. Warm water temperatures (over 80F/26.6C) and low wind shear are allowing Roke to intensify. Tropical storm conditions are expected at the base from Friday, Sept. 16 through Sunday, Sept. 18 as Roke continues on its westward track.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.



September 14, 2011

This infrared image of Tropical Depression Roke was taken by AIRS on Sept. 14 at 3:41 UTC. › View larger image
This infrared image of Tropical Depression Roke was taken on Sept. 14 at 3:41 UTC and shows that most of showers and clouds (purple) appear to be 100 nautical miles east of the center of circulation, indicating a disorganized storm. Orange indicates warm sea-surface temperatures.
Credit: NASA/JPL, Ed Olsen
NASA Infrared Eye Sees Tropical Depression Roke's Center Away from Strongest Rainfall

Sometimes it takes an infrared eye to see where the strongest showers and thunderstorms are within a tropical cyclone, and NASA's Atmospheric Infrared Sounder instrument or AIRS noticed that Tropical Depression Roke's strongest storms are about 100 nautical miles east of its center. That means that the storm isn't well-organized.

Tropical Depression Roke's maximum sustained winds were near 30 knots (35 mph/55 kmh) today, Sept. 14 at 11 a.m. EDT. It was 405 miles east of Kadena Air Base, Okinawa, Japan. That's near 25.7 North and 129.0 East. It was moving to the west-northwest at 17 knots (19 mph/31 kmh) and is expected to come together and intensify.

The AIRS instrument on NASA's Aqua satellite captured an infrared image of Roke on Sept. 14 at 03:41 UTC (Sept. 13 at 11:41 p.m. EDT). AIRS showed several areas of strong convection to the east of the center of the storm. Convection is rapidly rising air that condenses and forms clouds and showers. Those broken areas of strong convection are where AIRS measured the coldest cloud-top temperatures, indicating the thunderstorms are highest and rainfall is likely heaviest.

Strong convection surrounding a defined center is a sign of a strong tropical cyclone. That's not the case with Roke because its strongest convection is mostly to the east of the center. Roke currently appears far from being organized but conditions are expected to change that will allow Roke to strengthen over the next couple of days.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.



September 13, 2011

This infrared image of Tropical Depression Roke was captured by AIRS on Sept. 11 at 11:47 p.m. EDT. › View larger image
This infrared image of Tropical Depression Roke was captured on Sept. 11 at 11:47 p.m. EDT. The purple areas from the north to the southeast of the center of circulation indicate the coldest, highest cloud heights, where the heaviest rain was occurring in the depression.
Credit: NASA/JPL, Ed Olsen
NASA Satellite Sees Tropical Depression Roke Zig-Zagging in the Western North Pacific

Tropical Depression 18W was renamed Tropical Depression Roke after briefly reaching tropical storm status, while zig-zagging through the western North Pacific Ocean over the last day. NASA's Aqua satellite noticed that Roke's power is mostly on the eastern side of the storm's circulation.

When NASA's Aqua satellite flew over Tropical Depression Roke on Sept. 11 at 11:47 p.m. EDT, the Atmospheric Infrared Sounder (AIRS) instrument measured the temperatures in the storm's clouds and the sea surface temperatures surrounding the storm. The coldest, highest cloud heights are found from the north to the southeast of Roke's center, where the heaviest rain was occurring. Convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) is also beginning to build in a band of thunderstorms south of the center of circulation.

Roke is still over open ocean and far enough south of Iwo To that the island is not receiving any rainfall from the depression. Iwo To, however, may experience higher surf as Roke passes to its southwest and heads in a northwesterly direction. Roke is generating maximum wave heights of 16 feet.

At 11 a.m. EDT on Sept. 13, Tropical Depression Roke's maximum sustained winds were near 30 knots (34 mph/56 kmh). It was about 600 miles (965 km) east-southeast of Kadena Air Base, Okinawa, Japan, near 23.2 North and 138.2 East. Roke was moving to the northeast at 14 knots (16 mph/26 kmh), and is expected to turn to the northwest.

Roke is expected to gradually strengthen and become a strong tropical storm and pass near Kadena Air Base by the weekend.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.



September 12, 2011

MODIS image of TD18W › View larger image
NASA's Terra satellite captured this infrared image of Tropical Depression 18W on Sept. 12 at 9:20 a.m. EDT, when it had maximum sustained winds of 30 knots and was slowly moving through the western North Pacific Ocean.
Credit: NASA
NASA Satellite Sees Slow-Moving Depression 18W Tracking Through Western Pacific

The eighteenth tropical depression of the western North Pacific Hurricane season was born over the weekend and was captured by NASA's Terra satellite on its slow track to the west-northwest.

Tropical Depression 18W (TD18W) was born on Sept. 11 and by Sept. 12 it was still a depression. TD18W had maximum sustained winds near 30 knots (35 mph) at 11 a.m. EDT, Sept. 12, 2011. It was located about 500 nautical miles southeast of Kadena Air Base, Okinawa, and is moving to the west-northwest at 2 knots (3 mph). Minimum central pressure in the depression is near 1000 millibars.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite captured an infrared image of Tropical Depression 18W on Sept. 12 at 9:20 a.m. EDT that showed the strongest convection (rapidly rising air that forms the thunderstorms that make up a tropical cyclone) were mostly east of the center of the depression. The image showed the bulk of TD18W's cloud cover was east, and that's where the strongest thunderstorms and heaviest rainfall was occurring.

TD18W appeared to be slowing down, and consolidating. Another satellite image revealed the banding of thunderstorms around the low-level center of circulation, which indicates strengthening.

Later this week over the course of three days - Sept. 15, 16 and 17, slow-moving Tropical Depression 18W is forecast to slowly pass just southwest of Kadena Air Base.

Text credit: Rob Gutro,
NASA's Goddard Space Flight Center, Greenbelt, Md.