Stormy Start to weekend


Zoomed in Bermuda Weather Service radar image showing vigorous thunderstorm activity slowly moving across Bermuda, this is the last of three rounds of showers on Friday July 26th at about 5:16pm.
Zoomed in Bermuda Weather Service radar image showing vigorous thunderstorm activity slowly moving across Bermuda (marked by the white crosshairs), this is the last of three rounds of showers on Friday July 26th at about 5:16pm.

A series of weak surface troughs, enhanced by the semi-permanent Tropical Upper-Tropospheric Trough (TUTT) that typically sets up to the south and east of Bermuda, passed Bermuda Friday and today bringing heavy showers. These sometimes came with gusty winds and vivid lightning and thunder. Although generally isolated, they occasionally turned scattered in coverage at times meaning some areas of Bermuda got much more rain than others. Despite that, over the course of Friday and Saturday, 2-5inches of rain fell in Bermuda. This puts a huge dent in the developing dry spell and knocked high temperatures down nearer to climatological values.

These troughs are moving away from the island, taking their surface convergence with them, and the Bermuda-Azores high is retrograding to center itself in the central Atlantic as a dome of high pressure – this puts Bermuda to the west of the high, firmly under its western flank in deep southerly flow and more settled weather. Expect temperatures to return above normal as warm advection continues. For Monday into Tuesday – expect the Bermuda-Azores high to begin to weaken and flatten out into a ridge extending from Bermuda to the Azores rather than a dominating dome of high pressure. Light winds near the ridge axis could allow for convective showers to develop over Bermuda, possibly a Morgan’s cloud if the wind direction is right – something to monitor.

Wednesday into Friday sees the western side of the ridge become less defined as an easterly wave develops and meanders into the area – this may result in weather similar to Friday for the start of Cup Match. Keep monitoring the latest forecasts and advisory products from the Bermuda Weather Service for the latest official information for Bermuda.

Atlantic Analysis JULY 27 2013 2145UTC
My analysis of the northwest Atlantic showing the location of several troughs as red dashed lines, the blue arrows are rough streamlines of upper level winds indicating the location of the TUTT. The yellow circle shows the surface low that the National Hurricane Center is monitoring for tropical development with their latest chance of development in the next 48hours.

Meanwhile, Tropical Storm Dorian has bit the dust, so to speak. Succumbing to dry, stable air to the north, Dorian was not able to sustain its convection and so surface pressures near the center began to rise and, no longer producing westerly winds to the south of the center, Dorian degenerated into a Tropical Wave. Although there is a small window for Tropical Wave Dorian to redevelop into a Tropical Cyclone, it’s chances seem slim at this point.  The Tropical Wave is expected to continue following the well established flow south of the Bermuda-Azores high and pass north of the Caribbean. Although this means it avoids the islands, it also means the wave will enter an area of upper atmospheric winds from the TUTT that are not supportive of Tropical Cyclone development. Regardless of development, the wave could bring showers and gusty winds to the Windward islands, the Greater Antilles, the Turks and Caicos, and the Bahamas islands in the distant future if the wave holds together as a trackable feature.

Additionally, a non-tropical low has formed and is semi-detached from frontal boundaries over the warm waters of the Gulf Stream. The National Hurricane Center gives this area a 10% chance of becoming a tropical cyclone in the next 48hours. It is expected to quickly pass over the cooler waters of the Labrador current to its north before it has a chance to become tropical. Follow updates and products issued by the National Hurricane Center for the latest official information on tropical cyclones in the Atlantic.

Meanwhile, in the Pacific, Tropical Storm Flossie crossed from the Eastern Pacific into the Central Pacific, potentially threatening Hawaii as a weakening tropical storm or tropical depression in four to five days. An uncommon occurrence to follow as it develops.

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