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Forecast Change: Jasper Now Expected to Change Direction, Weaken

March 25th, 2009 Category: Tropical Cyclones

Track of Tropical Cyclone 23P (Jasper) - March 25th, 2009 © Univ. of Wisconsin

Track of Tropical Cyclone 23P (Jasper) - March 25th, 2009

TC 23P © JTWC

TC 23P

Tropical Cyclone 23P (Jasper), located approximately 205 nautical miles west-northwest of Noumea, New Caledonia, has tracked southeastward at 12 knots over the past six hours. Maximum significant wave height is 12 feet.

Observation of an exposed low level circulation center (LLCC) in recent animated multispectral satellite imagery lends confidence to the initial position. The current intensity estimate is consistent with recent agency Dvorak t-numbers ranging from 2.0 to 3.0.

The forecast philosophy for TC 23P has changed significantly since the previous warning. Increasing northwesterly vertical wind shear has displaced nearly all deep convection associated with this cyclone well to the southeast of the LLCC. The steering level for the storm has lowered as a consequence of this shear and a resultant ongoing weakening trend.

Therefore, the storm is now expected to follow strong southeasterly low to mid-level flow analyzed to the southwest. This southeasterly flow will begin to steer the LLCC equatorward by TAU 12.

As the storm turns equatorward, persistent vertical wind shear will offset the favorable influences of strong poleward outflow and warm sea surface temperatures, causing the system to weaken below the 35 knot warning threshold by TAU 36.

Tropical Cyclone 23P (Jasper) Forms in Pacific

March 24th, 2009 Category: Tropical Cyclones

Tropical Cyclone 23P (Jasper) - March 23rd, 2009

Tropical Cyclone 23P (Jasper) - March 23rd, 2009

Track of TC 23P - March 24th, 2009 © Univ. of Wisconsin

Track of TC 23P

Tropical Cyclone 23P (Jasper), located approximately 505 nautical miles northwest of Noumea, New Caledonia, has tracked east-southeastward at 13 knots over the past six hours, moving away from Queensland, Australia (visible at the bottom left). Maximum significant wave height is 12 feet.

Dvorak satellite intensity estimates of 2.5 from PGTW and 3.0 from ABRF and consolidating structure evident in recent microwave satellite imagery and scatterometer data indicate that the system has reached cyclone intensity.

Jasper is tracking east-southeastward along the western periphery of a subtropical steering ridge. This general motion is expected to continue through the next 12 hours. Thereafter, a second subtropical ridge to the southwest will induce a competing steering influence, slowing forward track motion and turning the system northwestward after TAU36.

TC 23P - enhanced image

TC 23P - enhanced image

The numerical model trackers, with the exception of WBAR and GFDN, are in fair agreement with this scenario. However, depictions of the exact track vary, and the current forecast lies close to the model consensus.

TC 23P is expected to intensify throughout the forecast period under the influence of dual-channel upper level outflow. Increasing vertical wind shear after TAU 24 should limit this intensification to a slower rate.

Tropical Cyclone 15P Forms in Pacific

February 17th, 2009 Category: Tropical Cyclones

Tropical Cyclone 15P - February 16th, 2009

Tropical Cyclone 15P - February 16th, 2009

Tropical Cyclone 15P, located approximately 120 nautical miles northwest of Noumea, New Caledonia, has tracked southwestward at 10 knots over the past 6 hours.

Maximum significant wave height is 10 feet.

Animated multispectral imagery indicates improving convection developing over a low level circulation center.

A WINDSAT pass indicates tight banding wrapping about the LLCC with deep convection on the southern periphery.

The upper-level environment has remained favorable with an anticyclone over the LLCC and enhanced poleward outflow caused by a shift in the upper-level trough/low northwest of the system.

Animated water vapor imagery reflects this improvement with expanding poleward outflow evident over the southern semi-circle.

SST is also favorable for further development.

TC 15P will track around a mid-level subtropical ridge that is weakening on its western flank and will allow the system to shift from a southwestward track to a southward track.

Continued upper level outflow and a favorable SST will allow TC 15P to intensify through TAU36 then begin to weaken as a mid-latitude trough interacts with the system.

source JTWC

Area of Convection Moves Closer to New Caledonia

February 4th, 2009 Category: Tropical Cyclones

Area of convection - February 3rd, 2009

Area of convection - enhanced image

Area of convection - enhanced image

An area of convection has persisted near 20.6S 162.1E, approximately 260 nautical miles west-northwest of Noumea, New Caledonia.

Recent animated infrared and water vapor satellite imagery show deep convection developing along a convergent band on the eastern periphery of a low level circulation center (LLCC).

Unflagged 20 to 25 knot winds have been shown near the center of the disturbance. Maximum sustained surface winds are estimated at 22 to 27 knots. Minimum sea level pressure is estimated to be near 1000mb.

The LLCC lies in an area of strong upper-level diffluence and increasing westerly vertical wind shear ahead of an approaching midlatitude trough.

Continued strong diffluence aloft may aid deepening over the next 24 hours, although the circulation is expected to transition into an extratropical low before sustained wind speeds approaching the warning intensity threshold of 35 knots.

Based on a less-than-optimal upper level environment and anticipated transition into an extratropical system, the potential for the development of a significant tropical cyclone within the next 24 hours is poor.

(See previous article and original article).

source JTWC

Area of Convection in Pacific Ocean Persists

February 2nd, 2009 Category: Tropical Cyclones

Area of convection, Pacific Ocean - January 31st, 2009

Area of convection, Pacific Ocean - January 31st, 2009

Location of Convection in Pacific - February 2nd, 2009 © JTWC

Location of Convection in Pacific - February 2nd, 2009

An area of convection has persisted near 12.9S 161.1E, approximately 640 nautical miles north-northwest of Noumea, New Caledonia.

The main image here shows the area of convection 36 hours ago, when it was located farther east. The image of the globe shows the system’s current location.

Animated METSAT imagery depicts a developing low-level circulation center (LLCC) with flaring deep convection located primarily over the western periphery of the disturbance.

An ASCAT pass shows 10 to 15 knot winds near the center of the tight, but elongated, LLCC.

The system is located in a region of strong, vertical wind which is limiting development at this time.

Area of convection - enhanced image

Maximum sustained surface winds are estimated at 10 to 15 knots. Minimum sea level pressure is estimated to be near 1002mb.

Due to the strong vertical wind shear and lack of persistent convection associated with the LLCC, the potential for the development of a significant tropical cyclone within the next 24 hours is poor.

source JTWC

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