Tropical Weather Discussion
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AXPQ20 PGUM 140046

Tropical Weather Discussion
National Weather Service Tiyan GU
1046 AM ChST Fri Jun 14 2024

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.




A surface trough extends from across the Philippines and enters
western Micronesia around 9N130E and continues towards Palau and Yap
Proper, before merging with the weak trade-wind flow and trade-wind
troughs that have broken off from the ITCZ in eastern Micronesia and
near Chuuk. The surface trough is similar to a weak monsoon trough
and is an early indication of a transition to the monsoonal pattern
that occurs during the summer. Light to gentle southwest winds extend
along the southern edge of the surface trough. Scattered showers
extend from Palau and northeast to Yap State and finally south of
Guam. The surface trough looks to linger in far western Micronesia
for at least the next couple of days as winds remain on the lighter
side as Palau and Yap remain in this early transitional phase.

The primary upper-level low is now located near 17N149E as it
continues to drift westward towards the northern islands of the
Mariana Islands, and will likely pass near and then west of Pagan and
Alamagan within the next 24 hours. Convection remains limited near
the center of the low, but the Global Lightning Detection (GLD)
network shows isolated thunderstorms south of the low and east of
Saipan and Tinian. Most of the showers and thunderstorms are found
farther to the southeast along and south of the TUTT axis that curves
southwest from across the Date Line at 17N180 to 11N170E and then
slowly curving northwest to the TUTT low. Part of this TUTT axis is
near the ITCZ discussed in more detail below. Another trough extends
southwest from the low passing south of Guam and ending in Yap State
near 9N143E, helping to enhance convection between Guam and Yap
Proper. The TUTT low will continue westward and move through and then
west of the Marianas, and will likely pass near and then west of
Pagan and Alamagan within the next 24 hours. Its presence will help
to bring showers and thunderstorms to the Marianas through Saturday,
with the potential for showers and thunderstorms decreasing Sunday as
the TUTT moves away from the Marianas.


The ITCZ still extends across eastern Micronesia, but has shifted
slightly northward as the bulk of the convergence between the
northeast and southeast trade winds is between 6N and 8N as it
extends from the Marshall Islands to Pohnpei and then becoming much
less defined near Chuuk. Scattered to numerous showers and isolated
thunderstorms are developing along or just north of the trade
convergence due to the upper-level support from the TUTT discussed
above. The ITCZ will continue to affect the region over the next
couple of days with some minor shifts to the north and south as
models show the ITCZ fragmenting by early next week, but still
supporting scattered showers across the region.