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AXPQ20 PGUM 051945

TWDPQ 



Tropical Weather Discussion

National Weather Service Tiyan GU

545 AM ChST Tue Jun 6 2023



Tropical Weather Discussion for the Western North Pacific between 

the Equator and 25N from 130E to 180. The following information is 

based on recent satellite imagery/data, weather observations, radar, 

and meteorological analysis.



...SIGNIFICANT/SPECIAL FEATURES...



TROPICAL AND MONSOON DISTURBANCES... 

A tropical disturbance, dubbed JTWC Invest 98W, is loosely centered 

280 miles north-northwest of Yap near 12N135E. Invest 98W is the 

subject of a Tropical Cyclone Formation Alert (TCFA), meaning there 

is a high likelihood that 98W will develop into a tropical cyclone 

during the next 24 hours. Overnight scatterometer data still reveals 

an elongated center, but is now oriented SW to NE. The system has 

been quasi-stationary the last 12-18 hours or so as the center 

jostles around and gravitates towards ephemeral convective pulses. 

Heavier showers are still by-and-large confined to the eastern sector

of the system, courtesy of juicy, convergent, southwesterly monsoon 

flow. 



...OTHER WEATHER SYSTEMS...



MONSOON TROUGH... 

98W anchors the eastern extent of the monsoon trough that spans much

of South East Asia.



TUTT... 

The TUTT (Tropical Upper Tropospheric Trough) curves westward from 

beyond the dateline to a series of TUTT cells, one near Wake Island, 

another northeast of Saipan near 21N153E, and a pair of less defined 

TUTT cells north and west of JTWC Invest 98W. Divergent flow south of 

the TUTT is enhancing convection across open waters east of the 

Marianas between 150E and the dateline. The westernmost TUTT cells may 

be introducing a wedge of dry air into Invest 98W as evidenced by 

CIMSS precipitable water satellite data. 



SURFACE TROUGH AND ATTENDANT CIRCULATIONS...

A weak circulation is evident on scatterometer and satellite near

Chuuk Lagoon. While the circulation itself is convectively inert, 

clusters of deep convection are flaring up in convergent trade flow

along its eastern sector, including islands of Chuuk State south of

Wenoagoon and much of Pohnpei State. A mesoscale convective system 

(MCS) is also seen along the northern periphery of the circulation

near 10N152E. The MCS may be getting enhanced by the TUTT pattern

to the north.



...ITCZ... 

The ITCZ (Inter-Tropical Convergence Zone) is perhaps best 

characterized as a series of trade- wind troughs transiting the region 

from near Kosrae to east of the Marshalls. Spotty deep convective 

towers are passing through at times with some enhancement from the 

TUTT to the north. Scatterometer data pegged a small pocket of fresh 

(17-21 kt) winds tucked along the north side of one of these troughs 

near Majuro and Wotje. 



...DISCUSSION...

JTWC Invest 98W is forecast to continue consolidating as the

elongated center cinches down and convection becomes more persistent. 

Palau and western Yap State can expect episodes of showery monsoon 

weather as 98W consolidates and gradually lifts farther away to the 

north. The monsoon trough should pivot northeastward in response to 

98W's motion. This northeastward pivot should allow a gentle trade-

wind regime to tuck in underneath the monsoon, with gentle trades 

edging into Palau and Yap early next week.



The circulation near Chuuk Lagoon and its accompanying trough will 

wander west or northwestward the next few days. Convection is likely 

to remain pinned along the eastern periphery as a prominent TUTT cell 

drifts west in tandem. Model guidance shows this circulation washing 

out near or south of Guam later this week. 



The ITCZ is likely to revive the second half of the week as low-level

convergence picks up and a slight surge in the trade flow occurs. This 

looks to bring a better chance of showers to central and eastern 

Micronesia south of 12N. Disturbances riding along the ITCZ may be 

enhanced by additional TUTT cell activity to the north. 



$$



Bukunt