Tropical Storm and Monsoonal Flow Collide Over Super-Heated Pacific to Dump Two Feet of Rain on Manila

Yesterday, tropical storm Trami churned through an abnormally hot Pacific Ocean toward an inevitable date with downpour over Taiwan and Southeastern China. There, a procession of tropical storms and monsoonal moisture had set off record floods which, by Tuesday, had resulted in the deaths of over 200 people. The now saturated region expects the arrival of Trami today, but not after the tropical monster, loaded with megatons of moisture, clashed with an already amped monsoonal flow to drench the Philippines as it emerged from a broiling Pacific Ocean.

Throughout the past month, an ocean heat dome had caused surface water temperatures to soar above 86 degrees Fahrenheit (30 degrees Celsius) over a vast swath of the Pacific Ocean just to the east of China and to the south of Japan and Korea. This powerful pool of latent Pacific heat was a major factor in the delivery of record heatwaves to China, Korea and Japan which resulted in thousands of hospitalizations and at least 100 lives lost. But yesterday, the heat and moisture rising off the Pacific would play its highly energetic part in an entirely different anomalous weather event — the inundation of the Philippine capital city of Manila.

Trami Collides with Monsoonal Flow to Produce Record Rainfall over Phillippines

Trami Collides with Monsoonal Flow to Produce Record Rainfall over Philippines

(Image source: NASA/Lance-Modis)

As Trami made her way over these hot and moisture rich waters, she grew in size until her cloud area covered a width of more than one thousand miles. Ocean temperatures soaring between 2 and 4 degrees (Fahrenheit) above average helped to pump its immense bulk full of moisture even as it became wrapped in a dense flow of monsoonal moisture proceeding from west to east off the continent.

By Monday, Trami was moving in from the east, lashing the Philippines with her dense, thunderstorm laden, spiral bands even as monsoonal storms came into collision with these bands from the west. The combination of a moisture rich tropical storm colliding with an equally rain dense monsoonal flow over a Philippines surrounded by anomalously hot water set off an extraordinarily intense rain event in which the capital of Manila was inundated by a powerful deluge.

Rainfall rates for this sprawling city hit a stunning 2 inches per hour and maintained that record shattering pace for almost twelve hours running. In total, more than 23.5 inches of rainfall was recorded at rain gauges across the capital. Many residents, whose homes were flooded in a rising rush of water, were forced to evacuate and initial reports indicate that at least 100,000 of Manila’s 12 million residents have now relocated to emergency shelters. So far, at least 8 deaths and millions of dollars in damages have been attributed to the storm. But with local levees and damns under threat of over-topping and collapse, the initial reports and estimates may just be the beginning.

Satellite and water vapor imagery taken on Tuesday showed rains continuing over the Philippines, albeit at a less intense rate, as Trami turned her great bulk of moisture northwestward toward the already soaked regions of Taiwan and southeastern China. Trami is expected to intensify into a category 1 Typhoon this afternoon and is likely to deliver severe rains and flooding to already soaked regions.

Trami Rakes Taiwan and Philippines

Trami Rakes Taiwan and Philippines

(Image source: NOAA)

You can see Trami raking both Taiwan and the Philippines with massive and rain-dense cloud bands in the most recent NOAA water vapor imagery. In this image, the storm appears to intensify as it bears down on the already storm-soaked shores of China and Taiwan.

Conditions in Context

The Philippines is hit by a total of 20 tropical cyclones each year. So heavy rainfall and floods are a regular aspect of life there. However, the nearly 24 inches of rainfall during a 12 hour period experienced yesterday is unprecedented, breaking even a number of Manila’s very high record rainfall totals. The conditions that led to these records, just one year after another severe rainfall event, include anomalous heating of the Pacific Ocean under a powerful Ocean Heat Dome during late July and early August, a rather strong and thick monsoonal flow that has tended to meander a bit further north than is usual, and a very large tropical cyclone fed by both the anomalous heat and added moisture.

Climate research has shown that we can expect more intense rainfall events worldwide as the hydrological cycle increases by 6% with a .8 degree Celsius temperature rise. Similar research has found evidence of more frequent tropical cyclones as oceans warm and seasons in which hurricanes may develop continue to lengthen. This region of the Pacific Ocean, in particular, has shown an increasing number of cyclones as Earth has continued its human-driven warming trend, with temperatures increasing by .2 degrees Celsius per decade over the last 30 years. Since the vast Pacific Ocean forms a kind of moisture trap in this steamy region, it is likely the area will experience some of the worst flooding and storm effects coming down the pipe due to human-caused warming.

Trami’s expected delivery of powerful storms to China and Taiwan will also, unfortunately, probably not be the last for this season. Water temperatures are still stunningly high and moisture flows from both the Indian Ocean and the Pacific are likely to churn out many more storms before the tropical cyclone season ends months from now.

Links, Credits and Hat Tips:

NASA/Lance-Modis

NOAA

Tropical Storm Trami Threatens Taiwan, China as the Philippines Floods

Commenter Steve

 

 

 

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9 Comments

  1. Steve

     /  August 21, 2013

    “Climate research has shown that we can expect more intense rainfall events worldwide as the hydrological cycle increases by 6% with a .8 degree Celsius temperature rise.” I’ve seen this line in a few of your posts. I am wondering if it is known how quick the hydrological cycle responds to the weather of the impact area. In the case of China, when they experienced temperatures far above .8 C of average temps over a long duration, would that effect the 6% increase during that prolonged of a heat event? I hope that question makes sense. Thanks for the work you put into this piece detailing how this storm came together.

    Reply
    • Local heating will increase the moisture gradient — ie evaporation/condensation/precipitation — for that region. In the case of heat domes, there’s a big pool of moisture left over either as the heat dissipates or condenses along the heat dome edge. In the case of the 6% number, it’s a global average based on hydrological cycle research. I’ll dig the paper up for your tomorrow, if you like. But that number will vary regionally and be influenced by prevailing conditions.

      So I’d think it a reasonable theory that this region of Asia may see a bit higher degree of variance during certain times of the year (monsoon etc). Unfortunately, we don’t have much science on how local conditions multiply or amplify prevailing global conditions.

      Reply
  2. Steve

     /  August 21, 2013

    Thanks Robert! No need for the extra work.

    Reply
  3. Steve

     /  August 26, 2013

    China keeps getting hammered. Another 16 inches of rain over a 24 hour period over the weekend. http://www.bbc.co.uk/news/world-asia-23838711

    Reply
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