Western Pacific Ocean – Typhoon Rai
Sunday, December 19, 2021

Current Snapshot

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By PDC’s Senior Weather
Specialist Glenn James

Tropical cyclone 28W (Rai)…is located approximately 353 NM south-southwest of Hong Kong

Northwest Pacific

Sustained 70 knot winds…with gusts to 85 knots (as of Warning Number 28)

According to the JTWC…the latest fix cycle confirms that typhoon Rai is past its peak and embarking on a permanent weakening trend. Rapidly warming tops and increasing asymmetry are apparent in animated water vapor imagery and visual imagery shows irregularities and fragmentation in the eyewall. A color composite verifies that dry air is making it into the core, and the system has lost a substantial amount of convection over the southeast quadrant. Although the eye has become cloud filled and fragmented, vigorous deep convection persists over three fourths of the storm and overshooting tops are still occurring in the southwest quadrant.

As the storm tracks poleward, it is moving into a region where ocean heat content plunges precipitously, and vertical wind shear increases steadily. The system is also heading directly into a river of brisk northeasterlies flowing out of a 1027mb high of continental polar air just south of shanghai. The extremely dry and cool air has brought temperatures all the way down to below 70F in Da Nang. Yet although the northeasterlies are pumping dry air into the core, they are also providing low level vorticity, that will sustain the vortex despite all the negative environmental factors working to kill it.

Typhoon 28W is on a permanent decline. Low ocean heat content, increasing vertical wind shear, and substantial dry air entrainment will kill the system as it rolls over and arcs around the western flank of the subtropical ridge. The same northeasterlies surging off the continent that will weaken the core convection, and be the primary factor in the system’s demise…will also induce enough spin to keep the vortex alive for another 72 hours, prolonging the process.

The system will also act as a sink for a recent vigorous surge in the northeast monsoon, drawing severe gale to storm force northeasteriles along the Vietnamese
coast. The severely hostile environment along the track of Typhoon 28W will prevent the system from even reaching Taiwan.