› Larger image This series of infrared images of Cyclone Narelle was taken over 6 days by the AIRS instrument that flies aboard NASA's Aqua satellite. It shows the growth into a cyclone and weakening back to a tropical storm. The purple areas are the coldest cloud top temperatures, and strongest storms with heaviest rainfall occurring in the cyclone. Top row L to R: Jan. 10 at 0623 UTC; Jan. 11 at 1759 UTC; Jan. 12 at 0605 UTC. Bottom row, L to R: Jan. 13 at 0647 UTC; Jan. 14 at 0553 UTC; and Jan. 15 at 0635 UTC. Credit: NASA JPL, Ed Olsen
› Larger image On Jan. 14, NASA's TRMM satellite saw mostly moderate rain (in green) southeast of Tropical Storm Narelle's center. An eye is no longer visible. The 3-D image shows some moderately high tops (around 10 km, shown in orange) remain in the area of moderate rain southeast of the center. Credit: SSAI/NASA, Hal Pierce NASA Satellites See Cyclone Narelle Torn Apart
NASA's TRMM and Aqua satellites showed how Tropical Cyclone Narelle has fallen far from being a powerful cyclone in the Southern Indian Ocean. A time series of infrared images from an Aqua satellite instrument provides a clear picture of Narelle's former power and its recent demise, while TRMM 3-D data showed falling cloud heights and weaker rainfall.
Narelle, once a powerful tropical cyclone with winds of 115 knots (~132 mph), was equivalent to a category 4 hurricane on the Saffir-Simpson scale. The storm has continued to steadily weaken as it made its way southward paralleling the coast of Western Australia.
The Tropical Rainfall Measuring Mission or TRMM satellite is a joint mission between NASA and the Japanese Space Agency. TRMM captured an image of Narelle at 04:04 UTC (12:04 pm Australian Western Standard Time) on January 14, 2013. At the time, the center of circulation was located about 350 km (~215 miles) due west of the coast of Australia, and the storm's intensity was down to a category 2 cyclone--equivalent to a category 1 hurricane. TRMM revealed that the intense rainbands previously surrounding the storm had greatly diminished in size and intensity and no longer wrapped completely around the storm.
TRMM saw mostly moderate rainfall located southeast of the center, and revealed that an eye was no longer visible. TRMM Precipitation Radar instrument data was used to create a 3-D image of the storm that showed most of the highest cloud tops had diminished, although some moderately high tops (around 10 km) remain in an area of moderate rain, located southeast of the center.
Infrared date from NASA's Aqua satellite provided a look at the life of Narelle, from its peak to its end. A time series of infrared images of Cyclone Narelle was taken over 6 days by the Atmospheric Infrared Sounder (AIRS) instrument that flies aboard NASA's Aqua satellite. AIRS data showed Cyclone Narelle's growth into a cyclone, where the storm developed a clear eye on infrared imagery. At the time of peak intensity, AIRS infrared data indicated that that thunderstorms around the eye were so strong and so high in the atmosphere, that infrared data indicated they had temperatures of -63F (-52C). By Jan. 15, AIRS data showed that Narelle had been blown apart by wind shear. AIRS data was captured on Jan. 10 at 0623 UTC; Jan. 11 at 1759 UTC; Jan. 12 at 0605 UTC; Jan. 13 at 0647 UTC; Jan. 14 at 0553 UTC; and Jan. 15 at 0635 UTC.
The Joint Typhoon Warning Center issued their final warning on Narelle on Jan. 14 at 2100 UTC (8 p.m. EST/U.S.). At that time Narelle's maximum sustained winds were near 35 knots (40 mph/64.8 kph), and it had become extra-tropical. The center was located near 29.9 south latitude and 110.2 east longitude. It was moving to the south at 18 knots (20.7 mph/33.3 kph).
On Jan. 15, wind shear had taken its toll on Narelle, and had blown the storm apart. AIRS infrared imagery from NASA's Aqua satellite on Jan. 15 showed that Narelle's remnants appeared more like a paint brush stroke from north to southeast, with no discernable center. Narelle's remnants were south of Perth, near Cape Leeuwin where they are expected to dissipate.
As Narelle continues to dissipate, the Australian Bureau of Meteorology maintained a strong wind warning for the following areas: Perth Local Waters, Lancelin Coast, Perth Coast and Bunbury Geographe Coast.
Narelle was the second cyclone to the form in the southern Indian Ocean this year. Cyclone Dumile passed east of Madagascar the first week of the year--and the fourth of the season. Typically there are about 9 tropical storms per season in the southern Indian Ocean, which runs year round from July through June.
› View larger NASA's Aqua satellite passed over Tropical Cyclone Narelle on Jan. 12 at 0615 UTC and Jan. 13 at 0655 UTC and captured these visible images of the storm. Narelle weakened and its eye had become cloud-filled. Credit: NASA Goddard MODIS Rapid Response Team
› Larger image NASA's TRMM satellite captured rainfall rates in Tropical Storm Narelle on Jan. 14 at 0404 UTC. A large area of moderate rainfall (green) was occurring south of the center of circulation, where rainfall rates were near 30 mm (1.18 inches) per hour Credit: NASA/SSAI Hal PierceNASA Sees Tropical Storm Narelle Winding Down Near Western Australia
Tropical Storm Narelle is growing weaker as it continues to track in a southerly direction parallel to the coast of Western Australia. NASA's Aqua and TRMM satellites captured visible data and rainfall rates on Narelle and noticed the storm was less intense than it was, however, warnings are still up as Narelle continues moving down the coast.
NASA's Aqua satellite passed over Tropical Cyclone Narelle on Jan. 12 at 0615 UTC (1:15 a.m. EST) and Jan. 13 at 0655 UTC (1:55 a.m. EST) and captured these visible images of the storm. The imagery on Jan. 12 showed that Narelle weakened and its eye had become cloud-filled. On Jan. 13, the imagery showed that the southeastern quadrant of the storm was over the northern coast of Western Australia.
NASA's Tropical Rainfall Measuring Mission (TRMM) satellite captured rainfall rates in Cyclone Narelle on Jan. 14 at 0404 UTC. There were no areas of heavy rainfall in the tropical storm. A large area of moderate rainfall was occurring south of the center of circulation, where rainfall rates were near 30 mm (1.18 inches) per hour. TRMM also showed that cloud heights had fallen below 10 kilometers (6.2 miles), indicating weakening in the uplift of air that helps create the thunderstorms that make up the cyclone. Infrared satellite imagery confirmed that the cloud tops were warming, which is another indication of falling cloud heights. The colder a cloud top is, the higher it is, and the stronger the thunderstorm. When cloud tops warm, they're not as high in the atmosphere, and the storms are weaker.
On January 14 at 1200 UTC (7 a.m. EST), Tropical Storm Narelle had maximum sustained winds near 45 knots (51.7 mph/83.3 kph). Narelle's center was located near 28.8 south latitude and 110.1 east longitude, about 430 nautical miles (494.8 miles/796.4 km) south-southwest of Learmonth, Australia and is moving to the south at 15 knots (17.2 mph/27.7 kph).
The Australian Bureau of Meteorology (ABM) noted on Jan. 14 that Narelle is not expected to produce gales on the coast. However, west coast tides are likely to rise above the normal high tide mark and coastal flooding is possible in low lying areas.
ABM issue a Strong Wind Warning on Monday, Jan. 14 for the following areas: Gascoyne Coast and Geraldton Coast. For Tuesday, Jan. 15, the Strong Wind Warning will be in effect for: Perth Local Waters, West Kimberley Coast, Gascoyne Coast, Geraldton Coast, Lancelin Coast, Perth Coast, Bunbury Geographe Coast and Leeuwin Coast.
Adverse atmospheric conditions and cooler sea surface temperatures are taking a toll on Narelle as it continues to move in a southerly direction and parallel the coast of Western Australia. Narelle is forecast to turn toward the southeast and become extra-tropical in the next day.
› Larger image NASA's Terra satellite passed over Tropical Cyclone Narelle on Jan. 11 at 0245 UTC and captured this visible image of the storm that has now formed a clear eye. Credit: NASA Goddard MODIS Rapid Response Team
› Larger image NASA's TRMM satellite captured rainfall rates in Major Cyclone Narelle on Jan. 11 at 0654 UTC. The red areas indicate heavy rainfall occurring at a rate of 2 inches (50 mm) per hour. Credit: NASA/SSAI Hal PierceNASA Gets an Eyeful from Major Cyclone Narelle Affecting Western Australia
Tropical Cyclone Narelle "opened" its eye while moving along the coast of Western Australia and NASA's Terra satellite captured a clear image of the well-formed storm center. Narelle is now a major cyclone on the Saffir-Simpson Scale.
NASA's Terra Satellite Gets an Eyeful
When Terra passed over Narelle on Jan. 11 at 0245 UTC the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument captured a visible image of the storm that clearly showed an eye had formed. Satellite imagery indicated that Narelle's eye was approximately 15 nautical miles (17.2 miles/27.8 km) wide. Satellite imagery also showed that Narelle had become more symmetrical and bands of thunderstorms had become more tightly wrapped into the center since Jan. 10.
Narelle Now a Major Cyclone
On Jan. 11 at 1500 UTC (10 a.m. EST), Tropical Cyclone Narelle's maximum sustained winds had increased to 115 knots (132.3 mph/213 kph), just as predicted by the Joint Typhoon Warning Center (JTWC). Narelle is now a major cyclone and a Category 4 hurricane on the Saffir-Simpson Scale. JTWC forecasters expect Narelle has now reached peak intensity and will begin to weaken hereafter as it moves parallel to the coast of Western Australia.
Narelle was located about 255 nautical miles (293.4 miles/472.3 km) north-northwest of Learmonth, Australia, near 18.3 south latitude and 112.6 east longitude. Narelle was moving to the southwest at 8 knots (9.2 mph/14.8 kph).
Narelle is moving along the northwestern edge of a sub-tropical ridge (elongated area) of high pressure that is centered over Western Australia. The JTWC forecast noted that Narelle is expected to round the western edge of this ridge over the next three days before it recurves southeastward. By Jan. 14, the JTWC expects the system will become a cold core low pressure system as it moves over cooler waters and encounters increasing vertical wind shear.
NASA Satellite Sees Narelle's Heavy Rainfall
NASA's Tropical Rainfall Measuring Mission (TRMM) satellite captured rainfall rates in Major Cyclone Narelle on Jan. 11 at 0654 UTC (1:54 a.m. EST). The heaviest rainfall was occurring at a rate of 2 inches (50 mm) per hour and stretched from north to west of the center of circulation.
This animated, 3-D flyby of Major Cyclone Narelle was created using data on Jan. 11, from NASA's TRMM satellite. Narelle's wind speeds were near 132 mph. A few thunderstorm towers in Narelle's eye extend to about 16km (9.9 miles) high (in red). Credit: NASA/SSAI, Hal Pierce
Warnings and Watches Posted
Until that time, however, warnings and watches are posted along the coastal areas of Western Australia. On Jan. 11, a Cyclone Warning was in effect for coastal areas from Mardie to Cape Cuvier. A Cyclone Watch is in effect for coastal areas from Cape Cuvier to Denham. A Blue Alert is effect for coastal and island communities from Mardie to Coral Bay including Onslow, Exmouth.
At 11 a.m. EST (1600 UTC) on Jan. 11, Onslow was reporting thunderstorms and sustained winds from the east-northeast. Onslow is a coastal town in the Pilbara region of Western Australia, located 1,386 kilometers (861 miles) north of Perth. Thunderstorms are expected to continue in the Pilbara region through Sunday, Jan. 13 as Narelle's center passes by while staying off shore. Onslow, Exmouth and other towns and cities in the Pilbara region are expected to clear by Monday, Jan. 14 as Narelle moves away.
For updates on warnings and watches, visit the Australian Bureau of Meteorology website: http://www.bom.gov.au/.
The latest forecast from the JTWC (as of Jan. 11) keeps the center of Narelle over open water and never making landfall in any part of Western Australia. Narelle is expected to pass the southwestern tip of Australia sometime on Jan. 16 and move in a southeasterly direction over the Southern Indian Ocean where it will dissipate.
› Larger image This visible image of Tropical Cyclone Narelle was captured by the MODIS instrument aboard NASA's Aqua satellite on Jan. 10, 2013 at 0625 UTC. Narelle developed the tropical cyclone signature shape with a tight rounded center and bands of thunderstorms wrapping around. Credit: NASA Goddard MODIS Rapid Response Team
› Larger image AIRS data of Narelle on Jan. 9 at 1811 UTC showed that the largest area of powerful thunderstorms (purple) were around the center, north and northwest of the center of circulation, an indication of where the heaviest rain was falling. Credit: NASA JPL, Ed OlsenNASA Sees Tropical Cyclone Narelle Approaching Western Australia Coast
NASA's Aqua satellite looked at Cyclone Narelle in visible and infrared light to understand the behavior of the storm. NASA's MODIS and AIRS instruments provided those data, respectively, and they showed that Narelle is gaining strength as it approaches the northern coast of Western Australia.
Watches and Warnings are posted for the western coast of Western Australia over the next several days as Narelle continues to move on a southerly track, where it is expected to remain at sea, but parallel the coast.
Current Australian warnings include: a Cyclone Warning is in effect for coastal areas from Whim Creek to Coral Bay, including Karratha, Dampier, Onslow and Exmouth. A Cyclone Watch is in effect for coastal areas from Coral Bay to Cape Cuvier. A Blue alert is in effect for the coastal and island communities from Whim Creek to Mardie, including Wickham, Roebourne, Point Sampson, Karratha and DampiFor updated warnings and watches, visit the Australian Bureau of Meteorology web page: http://www.bom.gov.au/australia/warnings/index.shtml.
When NASA's Aqua satellite passed over Narelle on Jan. 9 at 1811 UTC (1:11 p.m. EST/2:11 a.m. on Jan. 10, local time, Perth, Australia), the Atmospheric Infrared Sounder (AIRS) instrument captured data on the storm in infrared light. Infrared light shows temperature, and cloud top temperatures can indicate if clouds are reaching higher in the atmosphere (strengthening) or lower (weakening). AIRS data showed that the largest area of powerful thunderstorms were around the center, north and northwest of the center of circulation, an indication of where the heaviest rain was falling.
Another that flies aboard NASA's Aqua satellite called the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument captured a visible image of Tropical Cyclone Narelle as it was approaching the northern coast of Western Australia. The image was taken on Jan. 10, 2013 at 0625 UTC (1:25 a.m. EST/2:25 p.m. local time, Perth, Australia). The MODIS image revealed that Narelle developed the signature shape of a tropical cyclone with a tight rounded center and bands of thunderstorms wrapping into the center.
On Jan. 10 at 1500 UTC (10 a.m. EST/11 p.m. local time, Perth), Tropical Cyclone Narelle had maximum sustained winds near 80 knots (92 mph/148.2 kph). It was centered near 16.5 south latitude and 114.7 east longitude, about 370 nautical miles north of Learmonth, Australia. Narelle has been moving south-southwest at 10 knots (11.5 mph/18.5 kph). Narelle is churning up rough seas, as high as 32 feet (9.7 meters), which will likely cause coastal erosion and flooding. Narelle is expected to continue moving to the south-southwest toward Northwest Cape and gradually intensify.
Infrared imagery, such as what AIRS provides shows that a new feeder band of thunderstorms has formed to the south of the center. Infrared data showed that cloud tops around the center have cooled, indicating convection (rising air forming the thunderstorms that make up the cyclone) has strengthened, and cloud tops are higher and the storms more powerful. Microwave satellite data, which can see through clouds, showed that an eye was forming in the center.
The JTWC forecasters call for Narelle to continue intensifying as it moves south, and peak around 115 knots (132.3 mph/213 kph) sometime on Jan. 12 before weakening again.
New forecast guidance from the Joint Typhoon Warning Center (JTWC) now calls for the west coast of Western Australia to experience Tropical Cyclone Narelle's rainfall, gusty winds and rough surf. The JTWC forecast now takes Narelle close to the coast from north of Learmonth to the peninsula south of Perth, where it is now expected to make landfall in the South West region of Western Australia on Jan. 15 after tracking south through Geographe Bay.
› Larger image These two AIRS infrared images of Tropical Cyclone Narelle were captured on Jan. 8 at 1723 UTC and Jan. 9 at 0541 UTC. The very cold cloud top temperatures of -63F (-52C) appear in purple, indicating high, powerful thunderstorms with heavy rainfall. Credit: NASA JPL, Ed Olsen
› Larger image This AIRS near-infrared image (that appears like a visible image) of Tropical Cyclone Narelle was captured on Jan. 9 at 0541 UTC. The circulation center appears tight, with a large band of thunderstorms wrapping around from the south. Western Australia is seen southeast of Narelle. Credit: NASA JPL, Ed OlsenNASA Sees Tropical Cyclone Narelle Intensifying
Infrared and near-infrared NASA satellite imagery provided signs to forecasters that Tropical Cyclone Narelle is intensifying as it moves southwest paralleling Western Australia coastline. Warnings have been posted as Narelle nears.
The Australian Bureau of Meteorology (ABM) issued the following watch and warnings for Narelle on Jan. 9: A cyclone watch is in effect for coastal areas from Whim Creek to Coral Bay. A Blue alert is in effect for coastal and island communities from Whim Creek to Mardie, including Wickham, Roebourne, Point Sampson, Karratha and Dampier.
The ABM noted on its tropical cyclone warning website today, Jan. 9, that Tropical Cyclone Narelle is expected to strengthen as it moves toward the Northwest Cape. ABM said that gales with gusts to 100 kph are expected to develop in coastal areas between Whim Creek and Onslow including the Karratha area Friday morning (Jan. 11), then extend west to Exmouth and Coral Bay later Friday or early Saturday (Jan. 12). Thunderstorm activity is forecast to increase along the Pilbara coastline on Jan. 11, where some areas may experience heavy rainfall. On Saturday, winds are expected to increase along the western Pilbara coast.
NASA's Aqua satellite has been providing data to forecasters at the Joint Typhoon Warning Center. The Atmospheric Infrared Sounder (AIRS) instrument aboard Aqua has been capturing infrared and near infrared data that have shown colder cloud top temperatures and a more organized center of circulation in Narelle over the two days of Jan. 8 and 9.
The two AIRS infrared images of Tropical Cyclone Narelle were captured on Jan. 8 at 1723 UTC and Jan. 9 at 0541 UTC (12:41 a.m. EST/U.S.) and showed cold cloud top temperatures of -63F (-52C) indicating high, powerful thunderstorms with heavy rainfall over a large area. Infrared satellite imagery also showed tightly-curved, deep convective banding of thunderstorms wrapping into a well-defined low-level circulation center that was evident on AIRS near infrared imagery on Jan. 9 at 0541 UTC (12:41 a.m. EST/U.S.).
Near-infrared imagery looks like a visible image. That near-infrared image showed a tight circulation center with a large band of thunderstorms wrapping around from the south. Western Australia is seen southeast of Narelle. All of the AIRS imagery was created at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
On Jan. 9 at 1500 UTC (10 a.m. EST/U.S.), Tropical Cyclone Narelle was located near 13.5 south latitude and 115.9 east longitude, about 525 nautical miles (604.2 miles/972.3 km) north-northeast of Learmonth, Australia. Narelle was moving to the southwest at 6 knots (7 mph/11.1 kph) and generating waves up to 26 feet high (7.9 meters).
Narelle's maximum sustained winds were near 70 knots (80.5 mph/129.6 kph). Cyclone-force winds extend up to 25 nautical miles (28.7 miles/ 46.3 km) from the center, while tropical-storm-force winds extend up to 85 nautical miles (97.8 miles/157.4 km) from the center.
Tropical Cyclone Narelle is expected to continue moving slowly southwest along the northwestern edge of a strong subtropical ridge (elongated area) of high pressure. That ridge is currently located over Western Australia.
Narelle is expected to continue intensifying over the next two days as it moves closer to the coastline. The Joint Typhoon Warning Center noted that after passing Cape Leveque Narelle will start to weaken. In the meantime, residents in the warning and watch areas should expect deteriorating conditions.
› Larger image
NASA's TRMM satellite passed over System 98S on Jan. 7 at 4:01 a.m. EST/U.S. hours before it intensified into Tropical Storm Narelle. TRMM saw two bands of strong thunderstorms west and northwest of the center where heavy rainfall (red) was occurring. Credit: NASA/SSAI, Hal Pierce NASA Sees Tropical Cyclone Narelle Form in Southern Indian Ocean
The eighth tropical cyclone to form during the Southern Indian Ocean cyclone season formed from low pressure System 98S and became Tropical Cyclone Narelle. NASA's TRMM satellite passed over System 98S and saw the hallmark "hot towers" that indicated the storm would soon likely intensify into Tropical Storm Narelle.
NASA's Tropical Rainfall Measuring Mission (TRMM) satellite passed over System 98S on Jan. 7 at 0901 UTC (4:01 a.m. EST/U.S.) hours before it intensified into Tropical Storm Narelle.
TRMM's Precipitation Radar instrument captured estimates of rainfall occurring in the storm. TRMM noticed two bands of strong thunderstorms west and northwest of the center of circulation where rainfall was occurring at more than 2 inches/50 mm per hour. Some of those thunderstorms were "hot towers," or large towering thunderstorms.
A "hot tower" is a tall cumulonimbus cloud that reaches at least to the top of the troposphere, the lowest layer of the atmosphere. It extends approximately nine miles (14.5 km) high in the tropics. The hot towers in System 98S were over 9.3 miles (15 km) high. These towers are called "hot" because they rise to such altitude due to the large amount of latent heat. Water vapor releases this latent heat as it condenses into liquid. NASA research shows that a tropical cyclone with a hot tower in its eyewall was twice as likely to intensify within six or more hours, than a cyclone that lacked a hot tower. System 98S became Tropical Storm Narelle on Jan. 7 at 1800 UTC (1 p.m. EST/U.S.).
On Jan. 8, infrared satellite imagery showed that the low-level circulation center was consolidating (organizing). Just as the TRMM satellite showed improved convective (rising air that forms the thunderstorms that make up the tropical cyclone) banding in the western and northern quadrants of the storm on Jan. 7, infrared satellite data on Jan. 8 showed improved deep convective banding over the southeast quadrant of the system.
On Jan. 8 at 1500 UTC (10 a.m. EST/U.S.), Tropical cyclone Narelle had maximum sustained winds near 45 knots (51.7 mph/83.3 kph). The center of Narelle was located near 12.8 south latitude and 117.4 east longitude, about 605 miles north-northeast of Learmonth, Australia. Narelle was moving to the southwest at 9 knots (10.3 mph/16.6 kph).
Forecasters at the Joint Typhoon Warning Center (JTWC) take Narelle on a south-southwestward journey as a result of moving around the northwestern edge of a low-to-mid-level subtropical ridge (elongated area) of high pressure, located to the east and southeast of the system. That's because high pressure systems in the southern hemisphere rotate counter-clockwise.
JTWC forecasters expect that Narelle will continue to intensify and may reach wind speeds of 130 knots in three days as it nears Learmonth, Western Australia. The current forecast track, however, keeps the center at sea, but the eastern half of the storm is expected to impact the far western part of West Australia, including Learmonth. If the cyclone gets that strong, that would mean very rough seas and some coastal erosion, possible heavy rainfall and gusty winds for that area. Currently, there are no warnings in effect for Western Australia, but residents should monitor their local forecasts.