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Posts tagged Rarotonga

Tropical Cyclone Oli (12P) Expected to Intensify Steadily

February 2nd, 2010 Category: Tropical Storms

Tropical Cyclone Oli (12P) - February 1st, 2010

Tropical Cyclone Oli (12P) - February 1st, 2010

Enhanced image

Enhanced image

Track of TC 12P - February 2nd, 2010 © Univ. of Wisconsin

Track of TC 12P

Tropical Cyclone Oli (12P), located approximately 540 nautical miles north-northwest of Rarotonga, has tracked southeastward at 20 knots over the past six hours. The initial intensity of 50 knots is based on Dvorak intensity estimates ranging from 45 to 55 knots. Maximum significant wave height is 18 feet.

The system will continue to track along the southern periphery of the near equatorial ridge for the next 48 hours, then slow as the subtropical ridge to the east picks up the system and tracks it increasingly poleward.

All the while, the cyclone will continue to steadily intensify under improved upper level venting and low vertical wind shear. Sea surface temperatures will not fall below 26 degrees Celsius until near TAU 96, around the same time the cyclone will begin extratropical transition. Vertical wind shear will also elevate as the system gains latitude. Both of these factors will contribute to slow weakening beyond TAU 72.

This forecast has been shifted south of the last forecast in response to the cyclone trending southeastward over the past 12 hours. The track has also been slowed, especially in the later TAUs, in line with a slower model consensus.

Tropical Cyclone 21P (Ken) Intensifies Slightly, but Expected to Weaken

March 19th, 2009 Category: Tropical Cyclones

Tropical Cyclone 21P (Ken) - March 19th, 2009 © Univ. of Wisconsin

Tropical Cyclone 21P (Ken) - March 19th, 2009

TC 21P (Ken) - March 18th, 2009 © JTWC

TC 21P (Ken) - March 18th, 2009

Tropical Cyclone 21P (Ken), located approximately 265 nautical miles south of Rarotonga, in the Cook Islands, has moved southeastward at 12 knots over the past six hours. Maximum significant wave height at 190000z was 12 feet.

The system has maintained convection around its low level circulation center and has slightly increased intensity.

Animated multispectral satellite imagery shows that a front-like convergent line has formed on the north to northeast quadrant of the system.

Environmental analysis indicates TC 21P is rapidly approaching the baroclinic zone, characterized by increasing vertical wind shear and cold air advection.

The cyclone is expected to fully transition into an extra-tropical system within the next 24 hours.

Tropical Cyclone 21P (Ken) Remains Almost Stationary

March 18th, 2009 Category: Tropical Cyclones

Tropical Cyclone 21P (Ken) - March 18th, 2009 © Univ. of Wisconsin

Tropical Cyclone 21P (Ken) - March 18th, 2009

TC 21P (Ken) - March 17th, 2009 © JTWC

TC 21P (Ken) - March 17th, 2009

Tropical Cyclone 21p (Ken), located approximately 190 nautical miles west-southwest of Rarotonga, in the Cook Islands, has remained quasi-stationary over the past 6 hours. Maximum significant wave height is 10 feet.

Recent animated multispectral satellite imagery shows a partially exposed low level circulation center (LLCC) with open cell CU to the West of the LLCC.

Animated infrared imagery shows a cell of deep convection to the East of the LLCC with fragmented deep convective bands wrapping into the east side.

A QuikSCAT pass reflects a well formed LLCC with 35 knot unflagged winds circling the center.

Currently the LLCC is located near the 26C sea surface isotherm and is moving into unfavorable sea surface temperatures. Outflow has been hampered with the cross equatorial outflow channel having closed off.

TC 21P is currently beeing steered by the low-level ridge to the East but an approaching mid-latitude trough will become the dominant steering influence in the next 12 hours.

Ken will accelerate to the Southeast where it will begin extra-tropical (ET) transitioning. It is expected to maintain intensity as the approaching mid-latitude trough will enchance poleward outflow as the system moves over cooler water. The system will complete ET transitioning by TAU 36.

Tropical Cyclone Formation Alert in Pacific Ocean

March 17th, 2009 Category: Tropical Cyclones

Tropical Cyclone Formation © Univ. of Wisconsin

Tropical Cyclone Formation

Area of convection © JTWC

Area of convection

An area of convection is now located approximately 240 nautical miles northwest of Rarotonga, in the Cook Islands.

The formation of a significant tropical cyclone is possible within 180 nautical miles either side of a line from 18.1S 163.5W to 23.9S 160.9W within the next 06 to 24 hours.

Winds in the area are estimated to be 25 to 30 knots. METSAT imagery indicates that a circulation center is located near 18.9S 163.2W. The system is moving southward at 6 knots.

Animated infrared satellite imagery and a METOP-A image indicate a rapidly consolidating low-level circulation center (LLCC) with multiple deep convective bands spiraling into the center.

This system, like TC 20p, is developing from the mid-levels down to the surface. However, unlike 20p, this system has better radial outflow with more rapidly improving convective banding evident at this early stage of development.

Despite surface development lagging slightly behind convective organization, scatterometer data has increasingly supported a strengthening LLCC. A partial ASCAT image shows 25-30 knot northerly flow over the eastern semi-circle.

The overall environment is very favorable for further development. Upper-level analysis and animated water
vapor imagery indicate an anticyclone over the LLCC with very good poleward outflow enhanced by two upper-level lows (southwest and southeast of the system), as well as excellent equatorward outflow enhanced by strong cross-equatorial flow.

The SST of 29C, ocean heat content and a deep moisture envelope support continued consolidation. Maximum sustained surface winds are estimated at 25 to 30 knots. Minimum sea level pressure is estimated to be near 1000 mb.

Based on the favorable environment characterized by excellent outflow and a rapidly organizing LLCC, the potential for the development of a significant tropical cyclone within the next 24 hours is good.

Tropical Cyclone 20P (Joni) Expected to Weaken

March 13th, 2009 Category: Tropical Cyclones

Tropical Cyclone 20P (Joni) - March 13th, 2009 © Univ. of Wisconsin

Tropical Cyclone 20P (Joni) - March 13th, 2009

TC 20P - March 13th, 2009 © Univ. of Wisconsin

TC 20P - March 13th, 2009

Tropical Cyclone 20P (Joni), located approximately 390 nautical miles south of Rarotonga, Cook islands, has tracked southward at 16 knots over the past 6 hours.

Joni has maintained an initial intensity of 55 knots despite gradually degrading upper level conditions and decreased sea surface temperatures. Dvorak satellite intensity estimates are at 3.5 or 55 knots from PGTW and KNES.

The initial position is based on a series of microwave images, which suggest that the LLCC is tucked in under the western edge of the remaining deep convection.

Equatorward outflow has weakened over the past 12 hours as the upper level low to the east moved closer to the system. This low is expected to cut off equatorward outflow all together within the next 12 hours as it moves even closer.

From the West, a longwave trough will bring heightened vertical wind shear and drier air, and the mid-level reflection will accelerate the cyclone poleward. Sea surface temperatures will continue to drop below sustainable levels.

All of these factors will rapidly weaken Joni over the next day. Maximum significant wave height at 130600z is 12 feet.