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Hurricane Season 2011: Tropical Depression 1A (Northern Indian Ocean)
06.13.11
 
AIRS saw some strong thunderstorms in 1A that brought heavy rainfall to Bhojde, Gujarat, India. › View larger image
NASA's Aqua satellite AIRS instrument did see some strong thunderstorms in the Tropical Depression 1A on June 11 at 21:29 UTC that brought heavy rainfall and strong thunderstorms (purple) to region near the Gir Forest National Park and Wildlife Sanctuary National Park in Bhojde, Gujarat, India.
Credit: NASA/JPL, Ed Olsen
NASA Sees Arabian Sea Tropical Depression Fading

The low pressure system called System 98A was renamed tropical depression 1A over the weekend, and its strengthening was short-lived, just as it appears on NASA satellite imagery.

NASA's Aqua satellite passed over Tropical Depression 1A on June 11 at 21:29 UTC (5:29 p.m. EDT) as it still sat off of India's west-central coast. The Atmospheric Infrared Sounder (AIRS) instrument did see some strong thunderstorms in the depression at that time, that brought heavy rainfall to region near the Gir Forest National Park and Wildlife Sanctuary National Park in Bhojde, Gujarat, India.

By June 12 at 0600 UTC (2 a.m. EDT), the Joint Typhoon Warning Center issued their final advisory on Tropical Depression 1A, which only lasted as a tropical depression for about one day. At that time, the depression was about 315 nautical miles southeast of Karachi, Pakistan near 20.7 North and 70.5 East. It was moving northwestward near 6 knots (7 mph /11 kmh) and maximum sustained winds were near 30 knots (34 mph/55 kmh).

Tropical Depression 1A moved in a north-northwestward motion off the coasts of Maharashtra and south Gujarat and then move crossed the province of Saurashtra.

By Sunday, June 12, 2011 at 8:09 p.m. EDT, a weather reporter in the city of Mahabaleshwar in the Indian state of Maharashtra contacted NASA's Hurricane page and noted that the "system developed into a Tropical cyclone for a short time over Saurashtra, Gujarat, India. It seems to fading away now."

The center remnant low continued to move north-northwest staying in the Arabian Sea and just of the India coastline on June 12, and was expected to dissipate quickly. Satellite imagery from June 13 showed no organization and mostly scattered and disorganized clouds in the area where the remnant low was located.

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



June 10, 2011

MODIS capture System 98A and showed some very high thunderstorms south of the center of circulation. › View larger image
This image of System 98A was captured by the MODIS instrument on NASA's Aqua satellite on June 10 at 0839 UTC (4:39 a.m. EDT).It showed some very high thunderstorms south of the center of circulation. Those thunderstorms appeared to cast shadows on the lower, less powerful thunderstorms below.
Credit: NASA/NRL
Ripe For Development System 98A Soaks West Central India

West-central India has been receiving a lot of rain from the low pressure area known as System 98A since June 9. The latest imagery from NASA's Aqua satellite shows some very high thunderstorms indicating the storm may be strengthening.

On June 10 at 0839 UTC (4:39 a.m. EDT), the Moderate Resolution Imaging Spectroradiometer on NASA's Aqua satellite captured an image of System 98A. It showed some very high thunderstorms south of the center of circulation. Those thunderstorms appeared to cast shadows on the lower, less powerful thunderstorms below. The most powerful thunderstorms act as a heat engine to a tropical cyclone and are an indication of strong convection, and possible strengthening.

Reports from Mahabaleshwar, India on June 10 noted that heavy rain was falling since the morning (local time). No flood warnings have been issued, but local flooding continues to be a possibility with System 98A sitting west in the Arabian Sea. System 98A moved away from the west coast of India earlier this week and is now drifting east and back toward the coast.

The Joint Typhoon Warning Center noted that there's a "High Chance" that a tropical depression will develop from System 98A over the weekend and meander off-shore. That means more rainfall for Mahabaleshwar and Mumbai.

System 98A's winds are estimated between 18 and 33 knots, so on the low end it doesn't qualify for a tropical storm yet. It is moving to the east-northeast near 2 knots and is located near 18.4 North and 70.3 East. That's 150 nautical miles west-southwest of Mumbai, India.

Infrared satellite imagery shows thunderstorms along the southwestern edge of the low's center. Strongest thunderstorms are just to the west and south of the center.

A trough (elongated area) of low pressure has been preventing thunderstorm development in System 98A, but that trough is expected to move through the region, and allow the low to re-start generating convection (rising air that develops thunderstorms in a tropical cyclone).

Because of warm sea surface temperatures in the Arabian Sea and a forecast of decreasing wind shear, System 98A may become a tropical storm over the weekend.

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



June 9, 2011

AIRS image of 98A › View larger image
This image of System 98A in the Arabian Sea was taken on June 8 at 20:59 UTC (4:59 p.m. EDT) from the NASA AIRS instrument onboard NASA's Aqua satellite. It shows a large area of strong thunderstorms (purple) surrounding the center of circulation.
Credit: NASA JPL/Ed Olsen
NASA Satellite Imagery Reveals Arabian Sea's Low 98A Getting Organized Quickly

The low pressure system called 98A hung around the west coast of India last weekend and then drifted into the Arabian Sea where the warm waters and light winds are helping it strengthen. NASA's Aqua satellite provided an infrared look at the strong thunderstorms that have developed in its center since it moved away from land and now it's likely going to become a tropical depression.

NASA's Aqua satellite flew over System 98A on June 8 at 20:59 UTC (4:59 p.m. EDT) and captured an infrared image of the storm from the Atmospheric Infrared Sounder (AIRS) instrument. The AIRS instrument measures cloud top temperatures and the colder the temperature, the higher and stronger the thunderstorm. The imagery revealed that System 98A now has a large area of very cold, high, strong thunderstorms surrounding its center of circulation and more prominently around the southwestern quadrant of the low level center, indicating that it's strengthening.

On June 8 at 2230 UTC 6:30 p.m. EDT, the Joint Typhoon Warning Center (JTWC) noted that System 98A has a high chance of becoming a tropical storm.

Winds in the area are estimated to be between 28 to 33 knots (32 mph to 38 mph/52 kmh to 62 kmh), which why, based on the lower value, that it isn't yet classified as a tropical storm yet. System 98A has been quasi-stationary over the last day and is about 180 nautical miles west of Mumbai, India.

Late on June 8 (Eastern Daylight Time), Mumbai reported that sea level pressure had dropped by two millibars and was 999 millibars. Pressure drops indicate strengthening of a tropical cyclone.

The JTWC now gives System 98A a high chance of becoming a tropical storm because of increased convection, low wind shear, warm sea surface temperatures and decreasing atmospheric pressure.

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



June 8, 2011

AIRS captured System 98A's cloud temperatures and thunderstorms on June 8and saw a large area of strong convection (purple). › View larger image
NASA's Aqua satellite AIRS instrument captured an infrared look at System 98A's cloud temperatures and thunderstorms on June 8 at 08:47 UTC (4:47 a.m. EDT) and saw a large area of strong convection (purple).
Credit: NASA/JPL, Ed Olsen
NASA Imagery Sees a Re-Awakening of System 98A in the Arabian Sea

System 98A has been bringing rains, gusty winds and churning up the surf along the Arabian Seacoast of west-central India for days, and NASA satellite imagery confirms that it is getting organized now that it has moved into open waters.

NASA's Atmospheric Infrared Sounder (AIRS) instrument onboard NASA's Aqua satellite captured an image on June 8 at 08:47 UTC (4:47 a.m. EDT) of the hundreds of thunderstorms that make up the low pressure area called System 98A. The low pressure area has now moved to the west-southwest and away from Mumbai, India. In fact, today it is located about 200 miles west-southwest of Mumbai near 17.2 North and 69.8 East.

It appears that the warm waters of the Arabian Sea, and the freedom from land areas has enabled the convection (rapidly rising air that forms the thunderstorms that power a tropical cyclone) to strengthen. AIRS infrared imagery today shows a very large area of high, cold thunderstorm cloud tops mostly on the southwestern side of the center of circulation. That area has temperatures as cold as or colder (it's a benchmark) than -63 Fahrenheit/-52 Celsius. Those cold temperatures in cloud tops mean they're very high in the troposphere and the thunderstorms have a lot of uplift. It also suggests that they're heavy rainmakers.

Despite stronger convection, infrared imagery also showed that the low level circulation center is partially exposed to outside winds. Another factor that's not enabling the low to strengthen into a tropical storm is the presence of dry air that was seen yesterday. Dry air is still present to the northwest of the low, and dry air saps moisture out of the air and suppresses thunderstorm development. That could help explain why most of the convection is in the southern side of the low.

System 98A is drifting slowly to the northwest, and according to the Joint Typhoon Warning Center, its maximum sustained winds are between 25 to 30 knots (29 to 34/46 to 55 kmh). The Joint Typhoon Warning Center gives System 98A a medium chance of strengthening into a tropical storm in the next 24 hours.

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



June 7, 2011

This 3-D image from TRMM Satellite data showed that System 98A has several thunderstorm › View larger image
This 3-D image from TRMM Satellite data showed that System 98A has several thunderstorm "Hot Towers" that reached heights of about 17.5 km (~10.6 miles) indicating strong convection (red) and heavy rainfall around the storm's center.
Credit: SSAI/NASA Goddard, Hal Pierce
TRMM noticed that the majority of rainfall was moderate (yellow and green) between .78 to 1.57 inches per hour. › View larger image
TRMM analyzed the rainfall rates within System 98A on June 6 at 0550 UTC (1:50 a.m. EDT) and noticed that the majority of rainfall was moderate (yellow and green) between .78 to 1.57 inches (20-40 mm) per hour, with some isolated areas of heavy rainfall (red) over the Arabian Sea, falling at almost 2 inches (50 mm) per hour.
Credit: SSAI/NASA Goddard, Hal Pierce
NASA's TRMM Satellite Sees 10 Mile-High Thunderstorms in Arabian Sea Weather System

NASA satellite data revealed 10 mile high thunderstorms on System 98A, a low pressure areas lingering in the eastern Arabian Sea, off the central western India coastline that continues to generate heavy rainfall.

The Tropical Rainfall Measuring Mission (TRMM) satellite is managed by both NASA and JAXA, and captures rainfall data from space. When it flew over System 98A on June 6, 2011 at 0550 UTC it captured data on rainfall and cloud heights. TRMM's Precipitation Radar (PR) showed powerful thunderstorm towers within this possible cyclone pushing up heights above 17 km (~10.6 miles).

The radar imagery also showed the heaviest rainfall (at about 2 inches/50 mm per hour) was occurring over the open waters of the Arabian Sea, while light to moderate rainfall was affecting coastal India. Weather observations from Mumbai, India showed an increase in sea level pressure by one millibar over the last day, indicating weakening of the low pressure area.

On June 7 at 1800 UTC (2:00 p.m. EDT), System 98A had still not yet strengthened into a depression. It was located about 120 nautical miles west-southwest of Mumbai, India near 18.3 North and 70.9 East. The low-level center is still not well-defined, despite some of those strong, towering thunderstorms, mostly west of the center.

System 98A may not grow into a tropical storm because of several factors. Despite the fact that System 98A is sitting over very warm water (~30 C) which is a very favorable condition for its development, dry air is located to the northwest, and dry air saps moisture and energy from tropical cyclones. The system is also being battered by wind shear. Forecasters at the Joint Typhoon Warning Center today give System 98A a poor chance of developing further in the next 24 hours.

Text Credit: Rob Gutro/Hal Pierce, NASA's Goddard Space Flight Center, Greenbelt, Md.






June 6, 2011

AIRS shows a large area of strong thunderstorms around the center, and in that band south of the center of circulation. › View larger image
NASA AIRS imagery (taken from the Aqua satellite) from today, June 6 at 5:59 UTC (1:59 p.m. EDT) shows a large area of strong thunderstorms (purple) around the center, and a second area of strong thunderstorms in that band south of the center of circulation.
Credit: NASA/JPL, Ed Olsen
NASA Sees a Storm Stirring in the Northern Indian Ocean Tropics

A low pressure area near Mumbai, India has been showing signs of increased shower and thunderstorm activity on NASA infrared satellite imagery.

System 98A is a low pressure area located about 55 nautical miles southwest of Mumbai near 17.5 North and 72.1 East. Recent infrared imagery from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite has shown that cloud tops have been growing colder, indicating that convection is strengthening and the thunderstorm cloud tops are getting higher. Higher cloud tops indicate stronger uplift needed to create stronger thunderstorms with heavy rainfall.

Although the center of circulation is weakly defined, the main convection is building around it. There's also bands of thunderstorms around the southern edge of the storm, which indicates better organization. Those bands of thunderstorms are fragmented, however. Currently, the maximum sustained winds are estimated between 15 and 20 knots (17-23 mph/27-37 kmh).

The AIRS imagery from today, June 6 at 5:59 UTC (1:59 p.m. EDT) shows a large area of strong thunderstorms around the center, and a second area of strong thunderstorms in that band south of the center of circulation.

Two factors that help a tropical cyclone develop are present in the region where System 98A is located. The vertical wind shear remains low (5 to 10 knots/6 to 12 mph/9 to 19 kmh) and sea surface temperatures are warm enough to support strengthening into a tropical cyclone.

Currently, the Joint Typhoon Warning Center who is the forecast organization responsible for this region, gives System 98A a medium chance for developing into a tropical storm in the next 24 hours. Given its close proximity to land, residents of Mumbai should stay informed.

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