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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.