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Tropical Cyclone Narelle (08S) Current Intensity 75 Knots

15.5S 119.7E

January 10th, 2013 Category: Tropical Storms

Tropical Storm 08S – January 8th, 2013

Enhanced image

Track of Tropical Storm 08S - January 9th, 2013 © Univ. of Wisconsin

Track of TS 08S

Tropical Cyclone Narelle (08S) located approximately 500 nm north-northeast of Learmonth, Australia, has tracked south- southwestward at 06 knots over the past six hours. Maximum significant wave height is 28 feet.

The current intensity of 75 knots is based on a consensus of Dvorak satellite intensity estimates from the same reporting agencies. Recent animated infrared satellite imagery shows deep convection flaring over a well-defined low-level circulation center (LLCC), particularly along the northwestern quadrant.

The system is tracking south-southwestward along the northwestern periphery of a subtropical ridge that extends across central Australia. This ridge is expected to remain the dominant steering mechanism throughout much of the forecast period. As the system tracks closer to the ridge axis over the next 12 to 24 hours, it is expected to track a bit further westward before making a poleward turn after TAU 48.

Passage over very warm water, low vertical wind shear, and strong outflow aloft will allow the system to intensify significantly over the next 48 hours. After TAU 72, passage over cooler water and entrainment of drier and cooler air during the extended forecast period will result in steady weakening.

The dynamic models are in good general agreement through TAU 36, but continue to diverge beyond that point. NOGAPS and the UKMET model show a steady turn around the ridge axis and track the system inland as it undergoes extra-tropical transition in the extended period. GFS and GFDN depict a nearly straight poleward track with steady weakening and extra-tropical transition of a remnant low after TAU 120. The ECMWF model, which has been very consistent over the past several runs, shows the system tracking more slowly and farther westward than the other models, with a rapidly dissipating circulation following the lower level flow.

The current forecast is consistent with the GFS and GFDN scenarios, given expectations that the cyclone will remain very strong through TAU 96. However, if the system dissipates more quickly during the extended period than currently forecast, TC 08S may follow a slower and more westward track similar to the ECMWF forecast. Due to the continued spread in dynamic guidance after TAU 48, there is low confidence in the JTWC forecast track.

Tropical Cyclone Narelle (08S) Expected to Intensify

12.4S 123.9E

January 9th, 2013 Category: Tropical Storms

Tropical Storm 08S – January 8th, 2013

Enhanced image

Track of Tropical Storm 08S - January 8th, 2013 © Univ. of Wisconsin

Track of TS 08S

Tropical Cyclone Narelle (08S) located approximately 610 nm north-northeast of Learmonth, Australia, has tracked westward at 7 knots over the past six hours. Maximum significant wave height is 20 feet.

Animated infrared (IR) satellite imagery indicates a rapidly consolidating low-level circulation center (LLCC) located under a central dense overcast feature with improved deep convective banding over the western semi-circle of the system. An AMSU-B microwave image shows deep convection surrounding a formative microwave eye feature. There is good confidence in initial position based upon the eye feature in the microwave imagery.

TC 08S is located equatorward of the upper-level ridge axis and is under weak to moderate (10 to 20 knots) east-northeasterly vertical wind shear with improved poleward outflow into a deep midlatitude trough positioned west of Australia. The initial intensity is assessed at 55 knots based on congruent Dvorak intensity estimates of 55 knots.

Narelle is forecast to track south to southwestward under the steering influence of the low- to mid-level subtropical ridge positioned southeast of the system. Dynamic model guidance is tight agreement with the exception of the GFDN, which tracks the system well west of the other models and at slower speeds. Overall, there is high confidence in the JTWC forecast track. TC 08S is expected to rapidly intensify under favorable environmental conditions and reach a peak intensity of 130 knots by TAU 72.