Friday, August 09, 2013

Shanghai Blowtorch

If our stretch of 70 degree nights was annoying enough, how about Shanghai's stretch of 15 days in 18 of 100 degree or hotter weather?  Shanghai, which set a record for hottest day on record Wednesday at 105.4 degrees, has had temperatures at or over 90 degrees for 33 (yep, you read that right) straight days, with lows at or over 70 for 42 straight.

If it weren't for two thunderstorms in the afternoons of July 31st and August 1st, Shanghai would be looking at its eighteenth straight day of lows at or over 80 degrees.

This is in a location where the average high and low at this time of the year are 90 and 78. Tropical humidity is the norm in the summer, with nighttime lows regularly flirting with the upper 70's and low 80's and highs that consistently run a few degrees higher than us.  Humidity and warm nights aren't uncommon -- the persistent level of heat, however, is.

Parts of China have been slogging through their hottest July on record, with Shanghai near the epicenter for the brunt of heat.  A rather persistent ridge of high pressure has been parked near East China for much of the last six weeks, as mapped below. That ridge, while not as strong as ones that have brought record-setting warmth to Northern Canada, has allowed for lots of sun, and a west-southwest surface wind to provide additional warmth blowing into the city as the surrounding Pacific Ocean provides next-to-no relief.  Parts of South and East China, which rely on Pacific moisture for plentiful rains in July and August, have been in a prolonged dry spell thanks to this pattern.  The lack of monsoon type rains -- Shanghai averages over six inches of rain in each of the three summer months -- and the sunnier weather that the heat high is bringing -- is setting up a vicious circle of hot, hot, and hot.

Heat index values earlier today in Shanghai pushed 120 degrees as, despite the lack of rain, there's still a high dose of humidity around.

Shanghai is not alone. Reports of even higher temperatures near Shanghai have occurred in this stretch of heat.

Modeling suggests the heat ridge over China holds serve into next week, with a potential respite in the pattern as there may be a tropical cyclone that develops, moves into Southeast China, and turns north towards Shanghai to bring remnant rainfall late next week.