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Questions for Claire

Archives: October

Is the recent typhoon activity in the Western Pacific unusual or not?

Thursday, October 22, 2009 | 06:17 PM PT

Question submitted by Ross McKinnon
(Hainan, China)

First off - let me copy the entire e-mail that I got from Ross:
"I live on the Island of Hainan in the South China Sea, and have been here for the past seven years from my former home on Pender Is. BC. We are now just waiting for our 6th typhoon of the year, all in the past 8 weeks. This is 6 more than has ever occurred here before, so what is going on?"

Great question! Here's what I have discovered:

To date we have seen eight tropical cyclone, five of which became typhoons, two reaching Super Typhoon status, the strongest classification of tropical cyclones in the Western Pacific. But when we look at the numbers, 2009 has actually been slightly below average. So far we have seen 19 tropical storms in the Western Pacific, which is slightly behind the pace needed to reach the yearly average of 27. Despite the fact that 2009 has been below average for the season, the past month has been remarkable, with five of the eight storms making direct landfall in Asia.

What is behind this recent uptick in activity and why are all the storms seemingly coming at once, and late in the season?

The answer may be El Nino, which refers to a periodic change in the atmosphere and ocean in the Pacific. During El Nino, the waters in the central and eastern Pacific are warmer than normal, and the effects on global weather can be drastic and far-reaching.

According to forecasters in China, we see more cyclones later in the season during El Nino years in the Western Pacific, and they tend to form farther east. With the warmer sea surface temperatures during an El Nino event, this would allow these storms more time over open water to grow into large and powerful typhoons. In fact, we tend to see more "Super Typhoons" during El Nino years, and this is true again this year, as Choi-Wan and Melor both reached Super Typhoon status.

El Nino also is a likely culprit for the inactivity in the North Atlantic, since El Nino can cause more wind shear in the upper atmosphere, a condition that limits the ability of Tropical Cyclones to survive.

I have a painting commission in the works and I'd like to include a visual reference to diagrams of weather patterns related to the Vancouver region. Are there such visuals available online?

Thursday, October 8, 2009 | 01:25 PM PT

Question submitted by Janice
(Vancouver, BC)

Wow, first off - congratulations Janice.

Next visual representations of weather maps around Vancouver (all of Canada in fact) are available on line. The best place to go is the Environment Canada web site at http://www.weatheroffice.gc.ca/jet_stream/index_e.html.

Also to get good quality representations of cold fronts, warm fronts etc check out http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml

Note that there is one meteorological feature that is primarily only used on Canadian maps: a trowal, or a trough of warm air aloft (American's call it a warm occlusion).

What does dewpoint mean in the weather forecast? And what is the "DEW Line"??

Thursday, October 8, 2009 | 01:18 PM PT

Question submitted by Sharyn Pountney
(West Vancouver, BC)

Sharyn, the dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water. The condensed water is called dew. The dew point is a saturation point. When the dew point temperature falls below freezing it is often called the frost point, as the water vapor no longer creates dew but instead creates frost or hoarfrost by deposition.

The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity will decrease.

The dew point really won't be mentioned much in a forecast, but you may here the odd broadcaster mentioning the reading during their weather presentation, as an indication of how close a site may be to becoming saturated or "fogged in".

And in regards to the "DEW line": The Distant Early Warning Line, also known as the DEW Line or Early Warning Line, was a system of radar stations in the far northern Arctic region of Canada. I was lucky enough to work on the DEW line before it was essentially disbanded in the late 1990's.

Do you have an opinion yet, as to whether El Nino,or his evil sibling La Nina will prevail this coming winter (09-10) and what the consequences will be in either case?

Thursday, October 8, 2009 | 01:08 PM PT

Question submitted by Gregg
(Vancouver, BC)

Ah, El Niño! Gotta love this little guy!

First off, a definition: El Niño is the periodic warming of central and eastern tropical Pacific waters, which usually occurs on average every two to five years and typically lasts about 12 months.

And yes, most scientists now expect this El Niño event to continue developing during through the next several months, with further strengthening possible. So essentially the event is expected to last through winter 2009-10.

There's an excellent article on this at http://www.noaanews.noaa.gov/stories2009/20090709_elnino.html.

The big issue for us here on the west coast, with these events, is the change in the precipitation patterns - namely our snowfall patterns. Unfortunately there is very little concise evidence to show that we historically see either more or less snow during an El Niño event.