Flash flood warning through Tuesday

The National Weather Service based off of Tiyan, Guam reports that flash flooding due to excessive rainfall is expected through Tuesday morning due to a tropical disturbance expected to develop to the east of the Marianas. 

According to a flash flood warning issued by the NWS yesterday afternoon, from today through Tuesday morning, excessive runoff due to heavy rainfall may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations in Saipan, Tinian, Rota, and Guam. 

Flooding may also occur in poor drainage and urban areas as well as low-water crossings may be flooded as a result of the excessive runoff. 

The NWS noted that the heavy showers and thunderstorms expected through the next few hours is associated with a tropical disturbance expected to develop within the eastern sector of the monsoon trough near the far Northern Marianas.

NWS sees a continuous upward trend in rainfall, with amounts between 2 and 4 inches with locally heavier amounts in excess of 4 to 6 inches possible through Tuesday.

Due to this, NWS encourages everyone to monitor later forecasts and be alert for possible flood warnings. Be prepared to take action, especially for those living in areas prone to flooding, should flooding develop.

Lastly, if living near streams and rivers, prepare to move items away from stream and river banks. Make sure storm drains nearby are not clogged, especially in low-lying areas, the NWS stated. 

Meanwhile, according to Monday’s forecast, showers are likely and individuals in the Marianas could possibly experience a thunderstorm. South southeast winds are expected to be at 8 to 11 mph becoming west in the afternoon. 

On Tuesday, weather forecasts show scattered showers and thunderstorms. The day is expected to be mostly cloudy, with south southwest winds at 6 to 11 mph increasing to 12 mph to 17 mph in the afternoon. Winds could gust as high as 22 mph. 

As of 7am yesterday, a large trough which extends from about 3N136E to about 18N161E, with a weak circulation, was seen near 11N155E. The convergence ahead of the trough is producing scattered to numerous convection that extends northeast from east of the Republic of Palau and Yap State to east of the Mariana Islands.

NWS stated that A surface ridge extends southwestward from near Saipan across Yap and Palau, separating the southwest monsoon flow to the northwest and the large tradewind trough to the east. The ridge is helping to increase convergence within the monsoon flow, and ahead of the large trade-wind trough. 

The ridge is expected to slowly drift west and break down, especially up towards the Marianas allowing the large trade-wind trough to move west-northwest. This could lead to a circulation to develop near the Marianas and allow a southwest flow to develop across the Marianas.

The series of tradewind troughs are expected to continue to drift west with little change in intensity.