5. Typhoon OMAIS (Enteng/06w)                     Print this Article
>> May 16-23, 2004

Omais: contributed by the United States, is the Palauan word for 'wandering around.'


Typhoon Omais was the third of three significant tropical cyclones during May and occurred during a triple-storm outbreak together with Super Typhoon Nida and Tropical Storm 05W. This midget typhoon passed only a whisker's breadth away from Yap Island before recurving north and northeast and dissipating.

Storm Origins

At 0600 UTC 14 May a new area of convection was noted approximately 250 nm southwest of Chuuk. JTWC included this new suspect area in their STWO at 0600 UTC, 14 May, and assessed it as having a poor potential for development. Animated multi-spectral satellite imagery revealed a possible weak LLCC with loose, cycling convection. An upper- level analysis indicated a moderate environment with weak to moderate wind shear and good diffluence aloft. The potential was raised to fair at 15/0000 UTC after significant improvement in organization of the deep convection over a definitive LLCC had been observed. After a TCFA was issued at 15/2200 UTC, the initial warning on Tropical Depression 06W followed.

Synoptic History

At the time of the first warning Tropical Depression 06W was moving west at 14 kts, being located some 525 nm east of Palau. Continuing west, it was upgraded to tropical storm status at 16/1200 UTC. The MSW increased a little more to 40 kts and this intensity was maintained through much of the 17th. At 17/0600 UTC animated multi-spectral satellite imagery showed the system with a disorganized, partially- exposed LLCC with the deep convection blowing off to the west. The storm had turned to a northwesterly path, and this heading took it to within 140 nm of Yap at 17/1200 UTC. At this time, enhanced infrared satellite animations showed organizing deep convection over the LLCC, and Tropical Storm Omais began to rapidly intensify with the MSW upped to 60 kts at 1800 UTC. (Editor's Note: The system did not officially become Tropical Storm Omais until 0000 UTC on 18 May, when JMA upgraded it to a 35-kt tropical storm--considerably less than JTWC's estimated MSW of 60 kts.)

Having suffered badly from the passage of Typhoon Sudal only a month earlier, things were looking rather bleak for the island of Yap at 18/0000 UTC. The continued northwesterly heading brought the center to approximately 50 nm south-southeast of Yap. (At 18/0300 UTC Warning #9 was amended to mention that Omais had been relocated to a position about 60 nm directly south of Yap to tie in with fixes from microwave and multi-spectral imagery.) The public advisory at 18/0059 UTC said it all: "Damaging winds are imminent at Yap and neighbouring islands. Tropical Storm 06W is forecast to pass over or very close to Yap as a Category 1 typhoon this evening. Residents of Yap should complete preparations for destructive winds as soon as possible." However, Lady Luck was smiling down on Yap. At 0600 UTC Omais turned west-northwestward and accelerated to 11 kts, sparing the island a direct hit. Also, the fact that Omais was a midget tropical cyclone seems to have worked to Yap's advantage. The radius of gale-force winds was no more than 50 nm in the northern quadrants and 70 nm to the south. More importantly, the radius of destructive 50-kt winds was only 20 nm to the north, so likely Yap only received winds gusting to barely gale force as Omais passed by to the south.

Continuing west-northwestward, Omais was upgraded to minimal typhoon status at 1800 UTC on 18 May, and the MSW of 65 kts was to be the peak intensity per JTWC's warnings. This intensity was maintained through the 19th. Microwave imagery at 1200 UTC revealed a possible banding eye feature. At 19/1800 UTC Typhoon Omais responded to the weakening ridge to the northeast by decelerating to 5 kts and turning towards the north- west. Six hours later, the MSW dropped to 60 kts, and Omais was down- graded to a tropical storm while located approximately 390 nm south- southwest of Okinawa. A 19/2252 UTC SSM/I pass revealed a partially- exposed LLCC on the north side of the deep convection.

At 0600 UTC on 20 May Tropical Storm Omais turned north-northeastward, completing its recurvature and accelerating to around 12 kts. The MSW dropped rather quickly through the 20th and was barely of tropical storm strength by 0000 UTC the next day. Continuing to the north and north- northeast, the storm blew itself out at 22/0600 UTC when located 380 nm southwest of Iwo Jima. An extract from JTWC's final warning, issued at this time, concluded: "TD-06W has dissipated more rapidly than previously forecast. Animated multi-spectral and enhanced infrared satellite imagery indicates an area of convection with no identifiable low-level circulation center." The remnants eventually merged with a frontal system.

JTWC was the only warning agency to classify Omais as a typhoon, and JMA was the only other agency to upgrade the system to severe tropical storm status, i.e., winds greater than 48 kts. JMA's peak 10-min avg MSW was 50 kts with an estimated minimum CP of 985 hPa. The peak 10-min avg MSW estimated by NMCC and CWB was 40 kts, and the peak intensity from PAGASA was 35 kts during the time Omais/Enteng was within that agency's AOR. The cyclone remained outside HKO's area of warning responsibility throughout its entire lifetime.

Damage and Casualties

No damage or casualties are known to have resulted from Typhoon Omais.

(Report written by Kevin Boyle)

Source: Gary Padgett's Monthly Tropical Cyclone Summary - May 2004

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