Typhoon Threat in the Philippines This Week as Tropical Storm Rammasun Moves West

July 13, 2014

Talking Points

- May to strengthen to a typhoon early in the week

- Will likely affect the Philippines Tuesday and Wednesday

- PAGASA, the national weather agency in the Philippines, has named the storm "Glenda"

Tropical Storm Rammasun (Glenda) is churning in the western Pacific Ocean, not far from where Super Typhoon Neoguri first developed.

(RECAPS: Super Typhoon Neoguri | Photos)


Infrared Satellite

Infrared Satellite

Strengthening Forecast

Tropical Depression Nine strengthened back into a tropical storm on Saturday, after passing Guam, and became Tropical Storm Rammasun (Thai for the God of thunder).

Rammasun is forecast to strengthen Monday and Tuesday as it moves over very warm water in a moderately favorable atmospheric environment.

The national weather agency in the Philippines, PAGASA, has named this system Tropical Storm Glenda. PAGASA uses its own separate list of names for tropical cyclones crossing the Philippines and adjacent waters.


This Week: The Philippines, South China, Vietnam

Tropical Storm Rammasun may strengthen into a typhoon (equivalent to hurricane-strength in the Atlantic or eastern Pacific basins, with sustained winds of at least 74 mph) early in the week.

Vertical wind shear (changes in wind speed, direction with height; normally hostile to tropical cyclone development and intensification) increased somewhat near the storm Sunday, putting Rammasun in a less favorable environment for intensification. As a result, its forecast intensity has been reduced from earlier forecasts.

That said, its track westward or west-northwestward over the warm western Pacific Ocean would allow it to strengthen more rapidly if the wind shear were to lessen.

The key to the track is a steering upper-level ridge of high pressure to the north. It appears this ridge will hold firm, keeping Rammasun on a west-northwest path toward the Philippines, while sparing Taiwan.

It is far too early to determine the exact path of the storm. According to the National Hurricane Center, the average forecast track error for Atlantic tropical cyclones four to five days out ranges from 175 to 220 miles. Average errors in the Western Pacific are much larger.

The center of Rammasun may approach the northern or central Philippines by late Tuesday or Wednesday, most likely as a low-end typhoon or high-end tropical storm.

Interaction with land over the Philippines should weaken Rammasun, though it could gain or regain typhoon strength as it moves across the South China Sea in the general direction of southern China and Vietnam late in the week.

Interests in the Philippines, southern China and Vietnam should monitor the progress of this system closely. Taiwan is now outside the cone of uncertainty, but it's a good idea to stay abreast of any possible changes if you live there or have travel plans there.

The Philippines are among the most tropical cyclone-prone countries on Earth. Four typhoons made landfall in the Philippines in 2013, the most destructive of which was Super Typhoon Haiyan (Yolanda). 

(MORE: Philippine Typhoon History | Super Typhoon Haiyan Devastation)

Haiyan was the third Category 5 typhoon to make landfall in the Philippines since 2010, according to Weather Underground's director of meteorology, Dr. Jeff Masters. Conversely, only three hurricanes in recorded history have made a Category 5 U.S landfall.

MORE ON WEATHER.COM: Typhoon Neoguri Photos

People look at a landslide caused by heavy rain in Nago, Japan's southern island of Okinawa on July 9, 2014. (Jiji Press/AFP/Getty Images)

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