Weather tracker: unusual low pressure brings tornadoes to California

An unusually deep area of low pressure moved into California late on Tuesday. The low deepened quickly, reaching the threshold for “rapid cyclogenesis”, when a low deepens by at least 24 millibars (mb) in a 24-hour period (millibars measure the effective weight of the atmosphere pushing down on the Earth’s surface, due to gravity). A weather buoy in Monterey Bay reported a drop of 24mb in just 17 hours, with a minimum air pressure of 985mb recorded there.

A similar air pressure was recorded at San Francisco international airport, a March air pressure record for that site. The area of low pressure brought heavy rain to California, with some further flooding, along with strong winds. A gust of 102mph (164km/h) was recorded over higher ground to the north of Los Angeles. The strong winds resulted in power outages, and were potentially caused by a sting jet, although the details are uncertain until further research has been conducted. Additionally, the low also produced tornadoes on Tuesday and Wednesday. A tornado in Carpinteria, near Santa Barbara, damaged mobile homes on Tuesday. The following day, one person suffered minor injuries from a tornado in Montebello, south-east of Los Angeles. The tornado also damaged building roofs and cars during its path of over half a kilometre in length.

At the end of February, Cyclone Yuzu had officially formed off the west coast of Peru. This cyclone, although not making landfall, has led to excessive rainfall over the past couple of weeks over northern Peru. Flash flooding, landslides and mudslides have been a common theme over the last two weeks, leading to eight deaths and several collapsed buildings. Although the worst of the rainfall is expected to have passed, a state of emergency has been declared over many regions and will probably remain in place for several weeks. No such event has been recorded in the region for 40 years.

Southerly winds across the South China Sea and neighbouring countries brought an unseasonably warm airmass across parts of Vietnam, south-eastern China, South Korea and Japan this week. In northern Vietnam, maximum temperatures were over 10C warmer than normal for late March. Hòa Bình province, south-west of Hanoi, had temperatures of 41.4C (106.5F) on 22 March, with 40.5C in Nghe An province on 23 March.


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