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The Eye of Jangmi – September 28th, 2008

September 28th, 2008 Category: Image of the day

September 28th, 2008 - Eye of Super Typhoon JangmiJangmi

September 28th, 2008 - Eye of Super Typhoon Jangmi

The Eye of Jangmi - Detail

The Eye of Jangmi - Detail

The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather of a cyclone occurs. The cyclone’s lowest barometric pressure occurs in the eye, and can be as much as 15% lower than the atmospheric pressure outside the storm.

In strong tropical cyclones, the eye is characterized by light winds and clear skies, surrounded on all sides by a towering, symmetric eyewall. In weaker tropical cyclones, the eye is less well-defined, and can be covered by the central dense overcast, which is an area of high, thick clouds which show up brightly on satellite imagery.

Weaker or disorganized storms may also feature an eyewall which does not completely encircle the eye, or have an eye which features heavy rain. In all storms, however, the eye is the location of the storm’s minimum barometric pressure: the area where the atmospheric pressure at sea level is the lowest.

Eye Structure - © NOAA

Eye Structure - © NOAA

A typical tropical cyclone will have an eye approximately 30–65 km (20–40 mi) across, usually situated at the geometric center of the storm. The eye may be clear or have spotty low clouds (a clear eye), it may be filled with low- and mid-level clouds (a filled eye), or it may be obscured by the central dense overcast. There is, however, very little wind and rain, especially near the center. This is in stark contrast to conditions in the eyewall, which contains the storm’s strongest winds. Due to the mechanics of a tropical cyclone, the eye and the air directly above it are warmer than their surroundings.

While normally quite symmetric, eyes can be oblong and irregular, especially in weakening storms. A large ragged eye is a non-circular eye which appears fragmented, and is an indicator of a weak or weakening tropical cyclone. An open eye is an eye which can be circular, but the eyewall does not completely encircle the eye, also indicating a weakening, moisture-deprived cyclone. Both of these observations are used to estimate the intensity of tropical cyclones via Dvorak analysis. Eyewalls are typically circular; however, distinctly polygonal shapes ranging from triangles to hexagons occasionally occur.

While typical mature storms have eyes that are a few dozen miles across, rapidly intensifying storms can develop an extremely small, clear, and circular eye, sometimes referred to as a pinhole eye. Storms with pinhole eyes are prone to large fluctuations in intensity, and provide difficulties and frustrations for forecasters.

Hurricane Profile - © NASA

Hurricane Profile - © NASA

Small eyes—those less than 10 nmi (19 km, 12 mi) across—often trigger eyewall replacement cycles, where a new eyewall begins to form outside the original eyewall. This can take place anywhere from ten to a few hundred miles (fifteen to hundreds of kilometers) outside the inner eye. The storm then develops two concentric eyewalls, or an “eye within an eye”. In most cases, the outer eyewall begins to contract soon after its formation, which chokes off the inner eye and leaves a much larger but more stable eye. While the replacement cycle tends to weaken storms as it occurs, the new eyewall can contract fairly quickly after the old eyewall dissipates, allowing the storm to re-strengthen. This may trigger another cycle of eyewall replacement.

Eyes can range in size from 320 km (200 miles) (Typhoon Carmen) to a mere 3 km (2 mi) (Hurricane Wilma) across. While it is uncommon for storms with large eyes to become very intense, it does occur, especially in annular hurricanes. Hurricane Isabel was the eleventh most powerful Atlantic hurricane in recorded history, and sustained a large, 65–80 km (40–50 mi)-wide eye for a period of several days.

source Wikipedia

Super Typhoon Jangmi (19W) approaching Taiwan

September 28th, 2008 Category: Tropical Cyclones

September 28th, 2008 - Super Typhoon Jangmi approaching TaiwanJangmi

September 28th, 2008 - Super Typhoon Jangmi approaching Taiwan

Jangmi - Image Enhanced

Jangmi - Image Enhanced

Super Typhoon Jangmi churned toward Taiwan on Sunday, with winds of up to 227 kph and dumping torrential rains as it forced flight and work cancellations ahead of its expected landfall later in the day. Typhoon Jangmi, the season’s most powerful storm so far, was located 200 km southeast of the eastern Taiwan city of Hualien and moving northwest at 29 kph, according to Taiwan’s Central Weather Bureau.

Tropical Storm Risk showed the storm weakening after passing over Taiwan, but still moving in a northwest direction to make a second landfall in China. The storm’s approach prompted the CWB to issue sea and land warnings for the east coast of Taiwan. Some domestic and international flights were also cancelled, though many were still flying on Sunday morning.

The government also warned of the danger of mudslides, and television showed pictures of rough seas along the coast. Ahead of its arrival, the storm, the biggest so far of the season for Taiwan, was already bringing heavy rains to the north and east of the island, dropping more than 300 mm of rain in places and expected to eventually dump up to a metre in some mountainous areas.

China’s official Xinhua news agency said the fast-moving storm was expected to make landfall in south China’s Fujian province on Monday, bringing torrential rains to Fujian and neighbouring Zhejiang province.

JTWC Warning #18

JTWC Warning #18

It said local authorities called vessels to harbour and issued warnings of possible floods and landslides, and that navigation was suspended across the Taiwan Strait. In Zhejiang city of Wenzhou, about 110 tourists were stranded at a small island, Xinhua said.

Jangmi is the second major storm to strike Taiwan in the last two weeks, following the passage of slow-moving typhoon Sinlaku which drenched the island and killed 12 people earlier this month.

Typhoons regularly hit China, Taiwan, the Philippines and Japan from August until the end of the year, gathering strength from the warm waters of the Pacific of South China Sea before weakening over land.

source Reuters

Super Typhoon Jangmi (19W) – September 27th, 2008

September 27th, 2008 Category: Image of the day, Tropical Cyclones

September 27th, 2008 - Super Typhoon Jangmi - © JTWCJangmi

September 27th, 2008 - Super Typhoon Jangmi - © JTWC

Over the past 12 hours, Super Typhoon Jangmi has maintained strength while tracking west-northwestward at 13 knots. animated infrared satellite imagery and a 271134z SSMIS image depicted a round 18 nm eye with an intense, symmetric core of deep convection and excellent convective banding over all quadrants.

The primary models have shown increasing agreement with a recurvature scenario near tau 48, and increased spread in the extended period.

The latest 500 mb analysis depicts a poleward oriented sub-tropical ridge east-northeast of the system, and a weaker east-west oriented str northwest of Taiwan extending westward into central China.

Animated water vapor imagery indicates good radial outflow, although the system is beginning to develop annular characteristics with much of the convection now isolated to a broad band of deep convection surrounding the eye of the system.

There is excellent confidence in the current position and 12-hour storm motion which are based on microwave and infrared eye fixes. The current intensity is based on Dvorak estimates of 140 knots from RJTD and PGTW, AMSUB intensity estimates of 138 knots, and excellent aircraft reconnaissance reports of 130 knots near the center.

Taiwan’s Central Weather Bureau issued a land alert on Typhoon Jangmi after upgrading the storm to a Super Typhoon, as wind speeds accelerated to an estimated 227 kilometers (141 miles) an hour.

The eye of the typhoon was about 560 kilometers east-southeast of the southern coastal town of Eluanbi at 11:30 a.m. local time, the bureau reported on its Web site. The eye may move to 140 kilometers east of Eluanbi offshore by 11 a.m. tomorrow.

It issued alerts today warning of landslides, falling rocks and floods, adding to an alert sent yesterday for shipping vessels. Winds are already affecting the eastern and southern parts of Taiwan, the bureau said.

JTWC Warning #17

JTWC Warning #17

Jangmi may land in China on the night of September 29 after passing through Taiwan, the Fujian Meteorological Bureau said on its Web site today. The typhoon could severely affect the eastern Chinese province as it gains strength, it said. Rainstorms are forecast along the region’s coastal cities on September 29 and 30.

Jangmi is still a 135kt category 4 typhoon, but it’s possible it may be upgraded to category 5 in the next JTWC advisory.

source JTWC

Typhoon Jangmi (19W)

September 26th, 2008 Category: Tropical Cyclones

September 26th, 2009 - Typhoon JangmiJangmi

September 26th, 2009 - Typhoon Jangmi

Typhoon Jangmi - Image Enhanced

Typhoon Jangmi - Image Enhanced

Typhoon Jangmi (19W) has turned gradually poleward while rapidly intensifying over the past 12 hours. An increase in storm organization is witnessed by the appearance of a 30 nm eye in multispectral satellite imagery.

The current intensity estimate of 90 knots is consistent with Dvorak t-numbers of 4.0 from both PGTW and RJTD. Typhoon Jangmi is tracking toward a weakness in the subtropical steering ridge induced by a mid-latitude trough to the north. Upper level outflow remains very strong, particulary toward a tropical upper tropospheric trough (TUTT) cell to the northeast.

The forecast philosophy has not changed significantly since the previous issuance of the prognostic reasoning message. Typhoon Jangmi is expected to turn toward a more westward track over the next 24 hours as the mid-latitude trough to the north progresses eastward and subtropical ridging rebuilds on the poleward side of the typhoon. Typhoon Jangmi will then continue generally northwestward along the steering ridge periphery toward taiwan through tau 72. Upper level outflow is expected to remain strong and along track ocean heat content high, so further intensification is likely before the typhoon impacts any landmass. By tau 72, however, the storm circulation will likely interact with the Island of Taiwan, beginning a weakenening trend.

The current forecast is supported with good confidence by the available numerical model guidance, and lies slighlty equatorward of the consensus in the tau 0 to tau 72 period. Some erratic track motion may occur if the circulation moves farther northward and passes over central Taiwan in the tau 48 to tau 72 period.

In the extended period, a second mid-latitude trough will work to further weaken the subtropical steering ridge. As this weakness develops, Typhoon Jangmi may turn slightly poleward as it moves inland into southeastern China and begins to dissipate.

Although there is some disagreement among the models in the extended forecast track depiction, all show the circulation progressing well into China during this period.

source JTWC