Rain in Sight


Monthly Actual vs. Normal year to date precipitation total for the airport. Normals based off of 1979-2000 climate period as is the climate records from the Bermuda Weather Service. Where there is brown, there is a deficit; where there is blue, there is a surplus of precipitation.
Monthly Actual vs. Normal year to date precipitation total for the airport as of July 9th. Normals based off of 1979-2000 climate period as is the climate records from the Bermuda Weather Service. Where there is brown, there is a deficit; where there is blue, there is a surplus of precipitation.

After a wet start to the year, mostly in February, Bermuda has fallen behind in precipitation. The Bermuda-Azores high has held a persistent ridge across the western Atlantic for the second half of Spring. As of July 9th, the airport was 3.81″ behind the normal year-to-date total precipitation. The last several days have featured a few hit or miss, passing isolated showers – no tank rain. However, an approaching cold front may change that. Keep in mind that a month’s worth of precipitation is 3-5 inches, and a week’s worth is around an inch.

A cell of high pressure to the southwest of Bermuda briefly allowed a period of light northerly winds over the last few days as a weak cold front dissipated in the area. Isolated areas of convergence and less stable air in the area led to isolated showers and thunderstorms for the middle of this week. Winds have since backed to the west and increased to moderate.

This weekend, another weak front is expected to become stationary in the area rather than dissipate. By early-morning Saturday, the cold front to the near north should enhance local convergence enough to produce isolated showers, a band of showers with a chance for thunder is possible Saturday afternoon along or just ahead of the front itself – depending on how well the boundary holds together as it approaches. The front then becomes stationary near the island, oriented from west to east as a wave of low pressure develops offshore of Virginia on Saturday evening. This keeps a chance for isolated showers and a risk for thunder in the area through Sunday.

The general expectation is for around 0.50″ of rain to fall from showers on Saturday and Sunday, but over an inch of rain is possible depending on the exact track and location of the heavier showers and thunderstorms ahead of and along the front as it approaches and becomes stationary. Since it has been very dry lately, this rain is very welcome.

Winds shouldn’t become an issue around this front. Expect today’s moderate westerly winds to continue into Saturday morning, veering northwesterly Saturday afternoon, and becoming light behind the front Saturday night. There is a slight chance for winds to become gusty in and around showers or thunderstorms, mainly ahead of the front. Winds remain variable at times on Sunday, but mostly light.

Monitor the progress of this weather with the Bermuda Weather Service and keep an eye out for possible Small Craft Warning and/or Thunderstorm Advisory.

The Tropics

The tropical Atlantic continues a quiet stretch after mid-June’s Tropical Storm Bill – no tropical cyclone formation is expected in the next five days. Meanwhile, the entire Pacific ocean has become very active; earlier this week there were three typhoons simultaneously in the West Pacific, a tropical storm in the central pacific and four other tropical disturbances with potential for tropical cyclone development.

himawari-8_band_03_sector_02_20150708053000
Japan’s Himawari 8 satellite, the newest suite of sensors operationally observing the Earth caught (from left to right) Typhoons Linfa, Chan-hom, and Nangka on July 8th at 530UTC in its full disc visible band. This geostationary satellite has the highest spatial and temporal resolution of the current operational meteorological satellites in orbit. New York Times Article. NOAA is expected to launch a similar satellite next March – GOES R.

Part of this activity can be attributed to an unusually strong phase of the Madden-Julian Oscillation (MJO), another part to unusually warm equatorial Central and Eastern Pacific waters associated with El Niño, and yet another to the climatological upswing in West Pacific tropical cyclone activity this time of year. The Western Pacific is the most active region in the world for tropical cyclones and so it is not uncommon to have multiple intense cyclones at the same time. The MJO is a wave that circles the globe from west to east, and makes one revolution roughly every 30-60 days. It consists of a region of enhanced convective activity and a more inactive region. The amplitude of this enhanced and reduced convective pattern is typically highest over the Indian Ocean and West Pacific. Tropical cyclones are known to form more readily in the enhanced convective phase of the MJO. The warmer than normal equatorial Central and Eastern Pacific waters associated with El Niño is also known to aid in tropical cyclone development in those regions.

Linfa has since dissipated over southeastern China where it made a landfall as a category one equivalent typhoon. Chan-hom is approaching eastern China for a possible landfall near Shanghai and later likely impacting the Korean peninsula and Japan as a much weaker cyclone. Chan-hom became a typhoon near Guam, Rota and Saipan bringing torrential rains there, then passed between Okinawa and Miyakojima as a category four equivalent typhoon within near hurricane conditions on Okinawa. Nangka has weakened from a brief run at Super typhoon status yesterday thanks to a concentric eye-wall cycle and some increased wind shear. Nangka is expected to continue westward for the next few days before being steered northward – possibly threatening Japan.

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