Climatology of Tokyo

Tokyo lies in the humid subtropical zone or can be classified by the Koppen-Geiger scheme as Cfa.  This means Tokyo has generally, hot humid summers and mild winters with cool spells.    

Some meso-scale climate controls that affect Tokyo are location and a major ocean current.  Because Japan is an island it's climate is deeply affected by its location on the Pacific Ocean and the Sea of Japan.  The tropical weather from these bodies of water bring substantial amounts of rain into Tokyo.  Generally, the marked rainy season is early June, lasting about a month.  On average, five or six typhoons pass through Tokyo from early August to early September.  In the winter, a high pressure area develops over Siberia and a low pressure area can develop in the Pacific Ocean bring cold fronts into Tokyo resulting in lower, colder temperatures. Snowfall is sporadic, but does occur almost annually.  

The major ocean current that affects Tokyo is the Kuroshio current, also know has Black Current, which is also known as Japan current.  This warm water current flows northward on the Pacific side of Japan which warms Tokyo and surrounding areas of Japan.  

A micro-scale climate control of Tokyo is the urban heat island effect. According to the Tokyo Metropolitian Government,  the annual mean temperature has increased about 5.4 degrees F over the past 100 years.  The city has been cited as a "convincing example of the relationship between urban growth and climate." This can be attributed to Japan's fast growth rates in the late 19th and early 20th centuries.  Today, Japan is home to roughly 127 million people.  

This image shows the Kuroshino ocean current that affects Tokyo's climate.

blog.geogarage.com

This is a climate graph of Tokyo for the averages throughout the year. 

http://www.climatetemp.info/japan/tokyo.html

This is a weather graph of my weather station in November 2003.

This is a weather graph of my weather station in November 2011. 

When comparing November 2003 to November 2011 low temperatures, it appears the the lower temperatures are higher than they were eight years ago.  There is also less daily rainfall annually than in 2003, this could also be a very dry year for Tokyo and doesn't summarize the total changes in Tokyo's weather patterns.  

Comparison of Tokyo Weather to Tehran, Iran Weather

Tokyo is located 4,760 miles away from Tehran and both cities are located relatively on the same latitude coordinate (35° N).  Tokyo is located at 35° 41' 6 N and 139° 45' 5 E while Tehran is located at 35°41' N latitude and 51°26' E longitude.  Although they have close in latitude coordinates,  both cities weather and climate differ greatly.  

View Larger Map

shows the same coordinate plane that Tokyo (A) and Tehran (B) lie on 

Tehran is considered to have a semi-arid, continental climate, while Tokyo has a humid, subtropical climate. 

http://www.climate-charts.com/Locations/i/IR40754.php

http://www.climate-charts.com/Locations/j/JP47662.php

Tehran's geographic location largely defines the city's climate.  North of the city is the Alborz Mountains and to the south is desert.  Summers are incredibly hot and dry, receiving only about 9 inches of rain annually; compared to Tokyo where summers are very wet, receiving 60 inches of rain annually.  Fall, Winter and Spring bring about moderate temperatures but there is the occasional weather conditions that can be harsh.  

Because Tehran is inland and Tokyo is located on an island, a major difference between the two cities is that Tokyo receives typhoons annually and Tehran does not.  Tehran and Tokyo are similar in a sense that January is both the coldest month and the warmest months are either July or August.  But the actual temperature differences can range from 20 or 30 degrees.  

Tehran in the Winter

m.joseparla.com

Tokyo in the Winter

http://www.trekearth.com/gallery/Middle_East/Iran/East/Tehran/Tehran/photo223485.htm

Tehran in the Summer

http://karen-freshstrawberries.blogspot.com/2008/08/late-summer-greetings-from-very-muggy.html

Tokyo in the Summer

Tokyo Air Masses

As mentioned before, Tokyo lies in the humid subtropical climate zone. Because Japan is an island in the in the Pacific Ocean, it has some interesting weather patterns. In the summer, Tokyo is influenced by the maritime tropical air mass that are generated over warm coastal waters on the east coast.  In the fall, winter and spring maritime tropical and continental polar air masses interact which creates frequent midlatitude cyclones with cold and occluded frontal activity.  

source: csulb.edu
Air Mass Map

These air masses allow for Tokyo to get an average of 40-80 inches of precipitation a year.  The summer months get more precipitation than the winter months because of the effects of the Asian monsoon.  

source: Wikimedia Commons
Topographic Map of Japan

Tokyo is located in the central part of the archipelago (chain of islands) of Japan.  There are several mountains surrounding Tokyo including; Mount Mitake, Mount Kumotori, Mount Mihara, and Mount Takao.  There are two rivers that run through Tokyo, the Tama river and  Samuda river. Tokyo's topography allows for high levels of precipitation because of the very mountainous terrain.  



source:  www.jma.go.jp/en/g3/
Tokyo Weather Map


This is a current weather map of Tokyo for 6pm on November 1st.  It shows developing lows coming in from the southeast towards Tokyo, which means clouds will roll in over the city.  Since Japan is an island and in the middle of major oceanic currents,  a dense fog could settle over Tokyo.