Tropical Cyclones – Pacific Ocean
Sunday, December 12, 2021

Current Snapshot

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By PDC’s Senior Weather
Specialist Glenn James

Tropical cyclone 03P (Ruby)…is located approximately 474 NM northwest of Noumea, New Caledonia
Tropical cyclone 28W…is located approximately 340 NM southeast of Yap


Northwest Pacific

Tropical Cyclone 28W

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Sustained 40 knot winds…with gusts to 50 knots (as of Warning Number 1)

According to the JTWC…satellite imagery depicts a partially exposed low level circulation center, displaced just south of an expansive area of deep, persistent convection. The most
recent microwave image depicted the disorganized structure of the system convective core, with the circulation displaced to the south.

Environmental analysis reveals divergent easterly flow over top of the system, aiding the convective activity currently being seen, though overall outflow remains relatively weak at present, both poleward an equatorward. Sea surface temperatures are very warm and vertical wind shear  is low…leading to an overall favorable environmental assessment.

Tropical Depression 28W is expected to track west-northwestward through the duration of the forecast period, along the southern side of an extensive ridge entrenched to the north. Track speeds are forecast to remain relatively steady except for a brief slowdown between 48 and 72 hours, in response to a slight weakening of the steering gradient due to development of a weakness in the ridge to the north.

TD 28W is expected to cross through the southern Philippine Islands after 72 hours, and ultimately emerge into the Sulu Sea and track to near Palawan by 120 hours. Over the next 12 to 18 hours, the center is expected to further consolidate while moving under the deep convection…establishing a well defined core.

This will mark the start of a period of steady intensification to a peak of 85 knots by 72 hours. The bulk of the intensification is expected in the first 48 hours, as vertical wind shear remains below 15 knots and  outflow remains relatively high. By 72 hours, shear is expected to increase above 15 knots and the outflow will decrease as the upper-level flow shifts to a more easterly direction, cutting off the poleward outflow channel.

The system will weaken as it crosses through the Philippines, due to inflow and core disruption caused by interaction with the complex terrain features. Once back over water, the system will quickly intensify once more as the poleward outflow channel is reestablished



Southwest Pacific

Tropical Cyclone 03P (Ruby)

Sustained 65 knot winds…with gusts to 80 knots (as of Warning Number 5)

According to the JTWC…satellite imagery depicts a 120-nmdiameter central dense overcast feature obscuring the low-level circulation center. A microwave image reveals a small core of convection with a microwave eye feature, and spiral banding over the southern semicircle.

The recent rapid consolidation is attributable to favorable environmental conditions, specifically, robust poleward outflow into a deep upper-level trough positioned east of Australia, low vertical wind shear and warm sea surface temperatures.

TC 03P will rapidly intensify through 36 hours, with a peak intensity of 85 knots anticipated. There is some uncertainty in the actual peak intensity, with potential for a higher peak intensity near New Caledonia.

By 60 hours, the system will begin to interact with the subtropical westerlies and track over cooler sea surface temperatures. By 96 hours, TC 03P will encounter strong vertical wind shear (30-40 knots) with significantly cooler sea surface temperatures.

This will serve to rapidly weaken the convective structure and lead to subtropical transition. However, the system will remain a storm-force subtropical low as it approaches New Zealand.


North Indian Ocean

No tropical cyclones or areas of disturbed weather under investigation by the JTWC

South Indian Ocean

No tropical cyclones or areas of disturbed weather under investigation by the JTWC

Arabian Sea

No tropical cyclones or areas of disturbed weather under investigation by the JTWC