Featured Images

Hurricane Season 2009: Typhoon Choi-Wan (Western Pacific)
09.21.09
 
September 21, 2009, second update

NASA's AIRS instrument captured Choi-Wan's frigid cloud temperatureson September 18 at 12:29 p.m. EDT. > View larger image
NASA's AIRS instrument captured Choi-Wan's frigid cloud temperatures (-63F or colder in purple) on September 18 at 12:29 p.m. EDT (16:29 UTC). Choi-Wan had just started transitioning to an extra-tropical storm at this time.
Credit: NASA/JPL, Ed Olsen
Yellow-green areas in this image indicate precipitation or ice in the storm's cloud tops. > View larger image
This microwave image of Choi-Wan was created on September 18 at 12:29 p.m. EDT combining AIRS and AMSU data. Cold areas in this image (yellow-green) south of Japan (top right) indicate precipitation or ice in the storm's cloud tops. The purple area (around the eye) has the coldest cloud temperatures to -63F.
Credit: NASA/JPL, Ed Olsen
Typhoon Choi-Wan Has Gone Into The History Books

The once mighty Super Typhoon Choi-Wan that reached Category 5 strength on the Saffir-Simpson hurricane/typhoon scale has become extratropical and is fading in the northern Pacific Ocean. The U.S. Navy's Joint Typhoon Warning center issued a final warning on Saturday, September 19, when Choi-Wan was making the extra-tropical transition.

On Saturday, September 19, Choi-Wan still had maximum sustained winds of hurricane strength, near 86 mph, still at Category One typhoon strength. At one time, the storm's maximum sustained winds had clocked at 161 mph. On Saturday, it was located about 410 miles southeast of Tokyo, Japan and moving further into the open North Pacific Ocean near 21 mph.

On Friday, NASA's Aqua satellite flew over Typhoon Choi-Wan and captured infrared and microwave images on September 18 at 12:29 p.m. EDT (16:29 UTC). Microwave images are created when data from NASA's Aqua satellite Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) instruments are combined. These microwave images indicate where there is precipitation or ice in the cloud tops and the images from last Friday revealed Choi-Wan still had cold, high thunderstorms.

The infrared imagery revealed that there were also some towering, strong thunderstorms around Choi-Wan's center on Friday.

Over the weekend, Choi-wan lost strength in the adverse atmospheric conditions as wind shear battered the storm. Choi-wan made the transition to extra-tropical status over the weekend.

A conversion to "extratropical" status means that the area of low pressure (known as Choi-Wan) eventually loses its warm core and becomes a cold-core system. During the time it is becoming extratropical the cyclone's primary energy source changes from the release of latent heat from condensation (from thunderstorms near the storm's center) to baroclinic (temperature and air pressure) processes. When a cyclone becomes extratropical it will usually connect with nearby fronts and or troughs (extended areas of low pressure) consistent with a baroclinic (pressure) system. When that happens it appears the system grows larger while the core weakens.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center



September 18, 2009, second update

Choi-Wan's eye is now obscured by cirrus clouds, indicating that the typhoon's strength is waning. > View larger image
NASA's Terra satellite flew over Typhoon Choi-wan on September 17 at 9:15 p.m. EDT. Note that the eye is now obscured by cirrus clouds, indicating that the typhoon's strength is waning.
Credit: NASA/MODIS Rapid Response Team
Yellow-green areas indicate precipitation or ice in the cloud tops. The purple areas indicate temperatures to -63F. > View larger image
This microwave image of Choi-Wan was created on September 18 at 12:17 a.m. EDT combining AIRS and AMSU data. Cold areas in this image (yellow-green) stretch from Japan (top right) east (and out of range of the satellite swath) indicate precipitation or ice in the cloud tops. The purple area (around the eye) has the coldest cloud temperatures to -63F and suggests cloud heights to the 200 millibar level, near the tropopause.
Credit: NASA/JPL, Ed Olsen
Cold cloud tops (purple) of Choi-Wan colder than -63F to the warm ocean waters (orange and red) as warm as 82F. > View larger image
This infrared image from AIRS shows a stark contrast in temperatures from the cold cloud tops (purple) of Choi-Wan colder than -63F to the warm ocean waters (orange and red) as warm as 82F.
Credit: NASA/JPL, Ed Olsen
Typhoon Choi-Wan Swinging By Japan on Weekend

Typhoon Choi-Wan passed the island of Iwo To stirring up heavy surf, hurricane-force winds and torrential, flooding rains. This weekend, it will continue on its northeasterly track paralleling Japan, while its center remains in the open Western Pacific Ocean.

Microwave and infrared imagery from NASA's Aqua satellite during the early morning hours of September 18 revealed extremely high thunderstorms in Typhoon Choi-Wan as it passed the island of Iwo To and was approaching Chichi Jima.

NASA satellite imagery showed that the tops of the thunderstorms are so high they reached the tropopause, the level of atmosphere between the troposphere and stratosphere. Those high thunderstorms mean very heavy rainfall for the area underneath. The cloud tops extended to the 200 millibar level in the atmosphere where temperatures are as cold or colder than -63 Fahrenheit.

Microwave images are created when data from NASA's Aqua satellite Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) instruments are combined. These microwave images indicate where there is precipitation or ice in the cloud tops and the latest microwave image revealed Choi-Wan had cold, high thunderstorms.

On September 18 at 11 a.m. EDT, Choi-Wan was located 120 miles west-northwest of Iwo To, near 25.8 north and 139.4 east. It was moving north-northeast near 13 mph. Choi-Wan's maximum sustained winds were near 126 mph and those winds were still generating huge waves, as high as 41 feet.

AIRS Infrared satellite imagery showed that Choi-Wan has maintained a very well-defined eye with a secondary outer eyewall. The infrared imagery also showed the stark temperature contrast between the icy cloud tops in the storm against the warm waters in the Western Pacific Ocean that continue to power the storm.

The Joint Typhoon Warning Center (JWTC) noted their "environmental analysis indicates Choi-Wan has crested the western edge of the mid-level steering subtropical ridge axis in a corridor of low vertical wind shear and warm sea surface temperatures (well in excess of 28 Celsius or 82 Fahrenheit)."

The JWTC said that Choi-Wan may intensify a little over the next day because it's in a favorable environment. After that, the storm will begin weakening and transitioning into an extra-tropical storm.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center















September 17, 2009, second update

Image from TRMM showing Super Typhoon Choi-Wan's heavy rainfall on September 17 > View larger image
TRMM captured Super Typhoon Choi-Wan heavy rainfall on September 17 at 2:34 a.m. EDT. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches per hour. Red areas near Choi-Wan's center are considered heavy rainfall at almost 2 inches per hour.
Credit: NASA/SSAI, Hal Pierce
Visible imagery of Choi-Wan from NASA's Tropical Rainfall Measuring Mission satellite > Watch movie
This movie shows a blend between visible and infrared satellite imagery with an overlayment of precipitation from NASA's Tropical Rainfall Measuring Mission satellite. The rainfall in Choi-Wan's center early this morning, Sept. 17 was near 2 inches per hour (red).
Credit: SSAI/NASA, Hal Pierce
NASA's TRMM Satellite Sees Heavy Rainfall in Choi-Wan

NASA and the Japanese Space Agency's Tropical Rainfall Measuring Mission (TRMM) satellite flew over the center of Super Typhoon Choi-Wan at 2:34 EDT on September 17, 2009 and captured heavy rainfall around the storm's center.

TRMM rainfall images are false-colored with yellow, green and red areas, which indicate rainfall between 20 and 40 millimeters (.78 to 1.57 inches) per hour. Dark red areas are considered heavy rainfall, as much as 2 inches of rain per hour.

Rain rates in the center of the swath are from the TRMM Precipitation Radar (PR), the only spaceborne radar of its kind, while those in the outer portion are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS).

For more information about TRMM, visit: http://www.trmm.gsfc.nasa.gov/.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center























September 17, 2009

MODIS image of Super Typhoon Choi-Wan on September 17 > View larger image
NASA's MODIS instrument on the Aqua satellite captured Super Typhoon Choi-Wan on September 17 at 0340 UTC (Sept. 16 at 11:40 p.m. EDT), west of the Mariana Islands in the Pacific Ocean.
Credit: NASA, MODIS Rapid Response
AIRS image showing Choi-Wan's high thunderstorm cloud temperatures > View larger image
Aqua's Atmospheric Infrared Sounder (AIRS) instrument captured Choi-Wan's high thunderstorm cloud temperatures (in purple) were colder than minus 63 Fahrenheit. Choi-Wan's eye is clearly visible in this image.
Credit: NASA JPL, Ed Olsen
NASA's Aqua Satellite: Super Typhoon Choi-Wan Heading North

NASA's Aqua satellite again flew over Super Typhoon Choi-Wan late last night and captured visible and infrared imagery of the monster typhoon. Aqua's Atmospheric Infrared Sounder (AIRS) instrument and Moderate Imaging Spectroradiometer (MODIS) captured two different views of Choi-Wan's clouds as it heads north toward the island of Iwo To (formerly known as Iwo Jima).

Despite Choi-Wan's sustained winds weakening a little over the last 24 hours, AIRS imagery showed Choi-Wan's high thunderstorms had temperatures colder than minus 63 Fahrenheit indicating Choi-Wan was very strong tropical cyclone (Category 4 on the Saffir-Simpson Scale). Also on Aqua, NASA's Moderate Imaging Spectroradiometer (MODIS) instrument captured a stunning look at Super Typhoon Choi-Wan's clouds with a clear eye, indicating the storm's power.

At 11 a.m. EDT on September 17, Super Typhoon Choi-Wan had maximum sustained winds near 149 mph (130 knots), bringing the storm back down to Category 4 typhoon status. The center of Choi-Wan was located about 205 miles south-southwest of the island of Iwo To, near 22.0 north and 139.7 east, and was moving northwest at 9 mph. It continues to generate extremely high waves, up to 42 feet high and Iwo To can expect dangerous high and battering waves, heavy downpours and hurricane-force winds.

Choi-Wan has weakened a little but the U.S. Navy's Joint Typhoon Warning Center (JTWC) noted that the storm remains a "fully developed cyclone with a very distinct symmetrical eye." That eye is clearly visible in the imagery from NASA's Aqua satellite today. The JWTC also noted that "Animated water vapor satellite imagery shows some erosion of deep convection to the northwest quadrant of the system. However, environmental analysis indicates the system remains in a corridor of low vertical wind shear and warm sea surface temperatures."

Choi-Wan is moving northwestward along the western edge of a sub-tropical ridge of high pressure, which has a clockwise circulation. If you think of a clock, Choi-Wan would be positioned near 7 or 8 o'clock. It will continue moving further in a northerly direction before heading in an easterly direction (think of it approaching 10 and 11 o'clock heading towards noon).

Choi-Wan is expected to start weakening on Friday, September 18 and will transition to an extra-tropical storm thereafter.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center



September 16, 2009

TRMM captured Category 5 Super Typhoon Chan-Woi on September 16 with sustained winds estimated at 140 knots (~161 mph). > View larger image
TRMM captured Category 5 Super Typhoon Chan-Woi on September 16 (9:20 a.m. local time) with sustained winds estimated at 140 knots (~161 mph). The storm now had a near perfect eye (dark center) surrounded by a very intense eyewall (darker red semicircle indicating very heavy rain) on its western side.
Credit: NASA/SSAI, Hal Pierce
NASA's Terra satellite captured a view of Choi-Wan's clouds on September 16 at 3:25 p.m. local time. > View larger image
NASA's Terra satellite captured a view of Choi-Wan's clouds on September 16 at 3:25 p.m. local time west of the Mariana Islands in the Western Pacific Ocean.
Credit: NASA/JMODIS Rapid Response
AIRS captured this view of Choi-Wan's frigid thunderstorm tops after it reached Category 5 typhoon status. > View larger image
NASA's Atmospheric Infrared Sounder instrument on the Aqua satellite captured this view of Choi-Wan's frigid thunderstorm tops (colder than -63F) on September 15 at 11:59 a.m. EDT after it reached Category 5 typhoon status.
Credit: NASA/JPL, Ed Olsen
Super Typhoon Choi-Wan Makes Its Way Through The Western Pacific

Choi-Wan, which began as a tropical depression back on September 12 about 500 miles (~800 km) east-southeast of Saipan, became the third category 4 typhoon in the Pacific this year as it was approaching the Northern Mariana Islands on September 15 (local time). Today, September 16, Choi-Wan is a Category 5 typhoon.

The Tropical Rainfall Measuring Mission satellite (better known as TRMM) has served as a valuable platform for monitoring tropical cyclones since its launch back in 1997, especially over remote parts of the ocean.

TRMM captured its first image of Choi Wan at 23:34 UTC on September 13, 2009 as the storm was moving due west about 200 miles (~320 km) east-northeast of Saipan. The image showed the horizontal distribution of rain intensity inside the storm. Rain rates in the center of the swath were created from the TRMM Precipitation Radar (PR), the only spaceborne radar of its kind, while those in the outer portion were created from the TRMM Microwave Imager (TMI). The rain rates were overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS).

Although not fully formed on September 13, it was evident in the TRMM satellite imagery that Choi-Wan already had a well-defined eye structure with an eyewall wrapping all the way around the center except in the southeastern quadrant.

Associated with the areas of heavy rain are intense thunderstorms that are fueling the storm by releasing heat into its core. Rain features surrounding the eye appeared all tightly curved, which is consistent with a mature cyclonic circulation. At the time of that first image, Choi-Wan was still just a Category 1 typhoon with maximum sustained winds estimated at 65 knots (~75 mph) by the Joint Typhoon Warning Center, but it would quickly intensify into a Category 4 storm with sustained winds estimated at 120 knots (~138 mph) less than day later.

Choi-Wan passed through the Northern Marianas as a Category 4 storm on the afternoon (local time) of the September 15 before heading northwest into the Philippine Sea where it intensified even further into a powerful Category 5 Super Typhoon.

TRMM captured another image of Choi-Wan at 23:20 UTC on September 15 (September 16, 9:20 a.m. local time) as it was moving northwest through the eastern Philippine Sea after passing through the Northern Marianas Islands. The storm now had a near perfect eye surrounded by a very intense eyewall with very heavy rain on its western side. Overall the storm is also very symmetric both in its cloud and rain patterns.

This highly symmetrical structure is a manifestation of its extreme intensity and cyclonic structure as features are quickly wrapped around in a circular orientation. At the time of the second TRMM image, Chan-Woi was a Category 5 Super Typhoon with sustained winds estimated at 140 knots (~161 mph). TRMM is a joint mission between NASA and the Japanese space agency JAXA.

On September 16 at 11 a.m. EDT (1 a.m. September 17 local time) Choi-Wan still had maximum sustained winds near 161 mph, and was a Category Five typhoon. It was moving west-northwest near 8 mph. It was located about 335 miles south of Iwo To (formerly known as Iwo Jima) near 19.5 north and 141.5 east. The storm is expected to recurve to the north and remain east of Japan.

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



September 15, 2009

CloudSat's image of Choi-Wan late Sept. 14 showed hot towers on both sides of the eyewall (bright red bands). > View larger image
CloudSat's image of Choi-Wan late Sept. 14 showed hot towers on both sides of the eyewall (bright red bands) in the Aqua satellite AMSR-E instrument 89 GHz image. Image also shows an enclosed eye wall (red circle) around the center with orange and red reflectivities (intense convection and precipitation) extending outwards.
Credit: NASA JPL/Colo. State
Aqua's AIRS instrument captured Choi-Wan's frigid clouds, colder than minus 63 Fahrenheit (purple area). > View larger image
Aqua's AIRS instrument captured Choi-Wan's frigid clouds, colder than minus 63 Fahrenheit (purple area) on September 15 at 1:30 p.m. local time.
Credit: NASA/JPL, Ed Olsen
The TRMM satellite captured an image of Choi-Wan's rainfall on September 13, as it was approaching Super Typhoon status. > View larger image
NASA's TRMM satellite captured an image of Choi-Wan's rainfall on September 13, as it was approaching Super Typhoon status. Rainfall in some areas exceeded 50 mm/hr (almost 2 inches per hour!).
Credit: NASA/SSAI, Hal Pierce
Three NASA Satellites Get Awesome Views of Super-Typhoon Choi-Wan

NASA's Aqua, CloudSat and the Tropical Rainfall Measuring Mission (TRMM) captured stunning satellite images and different views of Super Typhoon Choi-Wan this week. Aqua provided cloud temperatures, CloudSat provided a side look into the storm at convection, precipitation and hot towers, and TRMM provided a look at the extent and intensity of rainfall in Choi-Wan.

NASA's Aqua satellite flew over Choi-Wan on September 15 at 1:30 p.m. local time, and captured an infrared image of the storm using the Atmospheric Infrared Sounder (AIRS) instrument. The infrared instrument provides valuable data on a tropical cyclone's cloud top temperatures. They're important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the more powerful it is, and the data helped forecasters see Choi-Wan's cloud tops were as cold as or colder than minus 63 degrees Fahrenheit (F).

AIRS infrared images depict different cloud temperatures in purple and blue. Those cloud that appear in purple on AIRS imagery have temperatures 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. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the cyclone. Areas that are false colored as purple, are where meteorologists would also find the "hot tower" clouds that the TRMM and CloudSat satellites see. In fact, in Choi-Wan, CloudSat identified several hot towers.

A hot tower is a tropical cumulonimbus cloud that penetrates the tropopause, i.e. it reaches out of the lowest layer of the atmosphere, the troposphere, into the stratosphere. In the tropics, the tropopause typically lies at least 15 kilometers (over 9 miles high) above sea level. These towers are called "hot" because they rise high due to the large amount of latent heat released as water vapor condenses into liquid.

NASA's CloudSat satellite completed an eye overpass of Super Typhoon Choi-Wan in the Western Pacific Ocean on September 15, at 0352Z (Sept. 14 at 11:52 p.m.). The CloudSat overpass shows the vertical cross section right through the center of the storm. The eye center is free of cirrus clouds with eye wall edges sloping outwards towards the top of the storm and with hot towers on both sides.

Natalie D. Tourville, of the Atmospheric Science Department at Colorado State University Fort Collins, Colo. is a member of the CloudSat team. Tourville said, "The storm has a well developed, fully enclosed circular eye wall (red circle in the image) around the eye center with intense convection and precipitation (orange and red reflectivities) extending outwards. The Aqua Infrared (AIRS) depicts cloud cover throughout the overpass but the CloudSat image reveals moats (convection free areas) containing a thick cirrus canopy between the spiral rain bands."

This is one a few inner eye images CloudSat has managed to capture of a Category 5 tropical cyclone.

Data from TRMM over flights are used in making the rainfall analysis at NASA's Goddard Space Flight Center in Greenbelt Md. The rainfall analysis showed that Choi-Wan is a large and well-organized. TRMM's Microwave Imager and Precipitation Radar instruments revealed that Choi-Wan has bands of heavy rainfall.

NASA's TRMM satellite captured an image of Choi-Wan's rainfall on September 13, as it was approaching Super Typhoon status. Rainfall in some areas exceeded 50 mm/hr, that's almost 2 inches per hour!

NASA satellites provide daily information to the National Hurricane Center, the Central Pacific Hurricane Center, and the U.S. Navy's Joint Typhoon Warning Center, all of whom forecast tropical cyclones.

For more information and updates about Choi-Wan's intensity and status, please visit: http://www.nasa.gov/mission_pages/hurricanes/archives/2009/h2009_Choi-Wan.html.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center



NASA's Terra satellite captured an image of Super Typhoon Choi-Wan on September 14 at 8:45 p.m. EDT. > View larger image
NASA's Terra satellite captured an image of Super Typhoon Choi-Wan on September 14 at 8:45 p.m. EDT (10:45 a.m. local time September 15) from the Moderate Imaging Spectroradiometer (MODIS) instrument. The eye of this powerful Category 4 storm is clearly visible.
Credit: NASA/MODIS Rapid Response
This forecast track takes Choi-Wan on a northwesterly direction over the next several days. > View larger image
This is a forecast track created on September 15 for Super Typhoon Choi-Wan, from the National Oceanic and Atmospheric Administration. It takes Choi-Wan on a northwesterly direction over the next several days.
Credit: NOAA
NASA Satellite Captures Super Typhoon Choi-Wan Heading for Agrihan and Alamagan

Choi-Wan is an extremely dangerous Category Four typhoon on the Saffir-Simpson Scale, and is expected to strengthen to a Category Five storm later today. NASA's Terra satellite revealed that Choi-Wan had a very clear eye as it passed overhead late last night, indicating a strong, well-organized typhoon.

The islands of Agrihan and Alamagan in the Western Pacific lay Choi-Wan's path today and a typhoon warning is in effect for Agrihan, while a tropical storm warning remains in effect for Saipan. Dangerous and powerful winds near 130 mph are expected today and tonight (local time) in Agrihan and Alamagan.

On Tuesday, September 15 at 11 a.m. EDT (that's Wednesday, September 16 at 1 a.m. local time, as they're 14 hours ahead of the U.S. East Coast) Super typhoon Choi-wan had maximum sustained winds near 155 mph. That's the border of a Category Four and Category Five Typhoon (Hurricane). Sustained winds in excess of 155 mph are classified as a Category Five. Choi-Wan's center was approximately 175 nautical miles north-northwest of Saipan near 18.2 north 144.7 east, and the storm has tracked west-northwestward at 9 mph. Choi-wan is creating huge waves, up to 38 feet high.

NASA's Terra satellite flew over Super Typhoon Choi-Wan late last night at 8:45 p.m. EDT (10:45 a.m. local time this morning), and the Moderate Imaging Spectroradiometer (MODIS) instrument captured a clear eye in this well developed cyclone.

The National Weather Service forecast office that covers the U.S. Territory noted in their forecast today, "Residents of Agrihan and Alamagan islands should be prepared for the possibility of a direct hit from typhoon Choi-wan this afternoon or evening...with winds rising to well over 100 mph possible. Preparations to protect life and property should be completed as soon as possible. Remain in a safe shelter throughout the storm."

The National Weather Service's local warning states: "Winds at Agrihan and Alamagan will rise to typhoon force this afternoon...and winds of 130 mph or higher are possible late this afternoon or evening if the eye of Choi-wan makes a direct hit. Such winds would be life-threatening and result in near-total property damage. For Agrihan and Alamagan...a storm surge of 12 feet or more is possible as Choi-wan passes this afternoon and tonight. "

At Saipan a storm surge of 1 to 3 feet above high tide is possible...with hazardous surf of 8 to 11 feet along west facing reefs this evening...building to 12 to 15 feet tonight. High tide is expected around 6 pm today...which is around the time of closest approach to Alamagan. In addition, Guam, Rota and Tinian are under a High Surf Advisory until 6 p.m. CHST Thursday, September 17. High surf will affect exposed reefs and beaches in the advisory area producing dangerous rip currents. Surf will be 10 to 12 feet on west facing exposures and 8 to 10 feet on south facing exposures tonight through Thursday.

Heavy rainfall is expected through Wednesday with storm totals of 3 to 5 inches possible at Saipan and as much as 6 to 10 inches at Alamagan and Agrihan.

For a look at local radar from Andersen Air Force Base, Guam: http://radar.weather.gov/radar.php?rid=GUA&product=NCR&overlay=11101111&loop=yes>http://radar.weather.gov/radar.php?rid=GUA&product=NCR&overlay=11101111&loop=yes.

Choi-wan is still moving northwest while intensifying. It is expected to reach Category Five status on the Saffir-Simpson Scale.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center



September 14, 2009

The yellow-green areas in this image indicate where there is precipitation or ice in the cloud tops. > View larger image
NASA's Aqua satellite AIRS and AMSU instrument data created a microwave image of Choi-Wan on September 13 at 2:11 p.m. EDT. The cold areas in this image (yellow-green) that stretch from right center, left of the small chain of islands, indicate where there is precipitation or ice in the cloud tops. The purple area (far right) has the coldest cloud temperatures to -63F and suggests cloud heights to the 200 millibar level, near the tropopause.
Credit: NASA/JPL, Ed Olsen
NASA's AIRS instrument captured this impressive image of Typhoon Choi-Wan on September 14 at 11:05 p.m. EDT. > View larger image
NASA's AIRS instrument captured this impressive image of Typhoon Choi-Wan on September 14 at 11:05 p.m. EDT. The white area is outside the view of the satellite instrument as it passed over the storm from space.
Credit: NASA/JPL, Ed Olsen
Typhoon Choi-Wan Triggers Tropical Storm Warnings for U.S. Commonwealth of No. Mariana Islands

Microwave imagery from NASA's Aqua satellite revealed extremely high thunderstorms in Typhoon Choi-Wan as it began passing the island of Sai-Pan in the Western Pacific Ocean. The U.S. National Weather Service has already issued a tropical storm warning and a typhoon watch for Tinian, Saipan and Agrihan in the Northern Mariana Islands.

Saipan is the largest island and capital of the U.S. Commonwealth of the Northern Mariana Islands. The Northern Marianas are a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean. In the year 2000, the island chain was home to more than 62,000 residents. The National Weather Service issues advisories for them, because they are a U.S. Commonwealth.

NASA satellite imagery showed that the tops of the thunderstorms are so high they reached the tropopause, the level of atmosphere between the troposphere and stratosphere. Those high thunderstorms mean very heavy rainfall for the area underneath. The cloud tops extended to the 200 millibar level in the atmosphere where temperatures are as cold or colder than -63 Fahrenheit.

Microwave images are created when data from NASA's Aqua satellite Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) instruments are combined. These microwave images indicate where there is precipitation or ice in the cloud tops and the latest microwave image revealed Choi-Wan had cold, high thunderstorms.

On August 14 at 11 a.m. EDT, Choi-Wan was located 105 miles east-northeast of Saipan, near 16.2 north and 147.3 east. It was moving northwest near 5 mph. The storm has intensified over the last six hours in an area with warm waters and low wind shear. Choi-Wan's maximum sustained winds were near 90 mph and those winds were kicking up very high waves, as high as 29 feet. The typhoon is expected to pass north of Saipan Tuesday morning.

Residents of Saipan is already experiencing gusty winds and rains as the Choi-Wan passes to the northeast, and dangerous surf is expected along the shorelines. For a look at local radar from Andersen Air Force Base, Guam: http://radar.weather.gov/radar.php?rid=GUA&product=NCR&overlay=11101111&loop=yes>http://radar.weather.gov/radar.php?rid=GUA&product=NCR&overlay=11101111&loop=yes.

Storm surge and inundation of 3 to 5 feet above high tide is possible as Choi-Wan passes with hazardous surf of 8 to 12 feet along west facing reefs this evening...building to 13 to 16 feet tonight. High tide is expected around 6 p.m. local time on Tuesday.

The National Weather Service also expects locally heavy rainfall through early Wednesday Morning with totals of 3 to 5 inches on Tinian and Saipan and as much as 6 to 10 inches possible on Agrihan and Alamagan.

The National Weather Service issued a special bulletin at 10:09 p.m. local time (CHST) today, September 14: "The 24 hour pressure fall at Saipan airport was 7.5 millibars. Pressure falls are likely even larger at islands north of Saipan. This shows not only the continuing approach of Choi-Wan but also its continuing trend for intensification. It has been several years since a significant typhoon has struck the Marianas. Especially for Alamagan...beware of a sudden drop in winds. This may be the eye rather than the end of the storm. In this case winds will return just as suddenly from the opposite direction. Choi-wan will pass very close to Alamagan Tuesday afternoon."

Choi-Wan is the fifteenth tropical cyclone in the western Pacific Ocean this season. The sixteenth, Tropical Storm Koppu is poised to make landfall in China in the next day or two.

For local weather forecasts and updated weather watches and warnings, visit the National Weather Service forecast page for Saipan: http://forecast.weather.gov/MapClick.php?zoneid=GUZ004.

Text credit: Rob Gutro, NASA/Goddard Space Flight Center