WRUF Weather

WRUF Tropical Update: Calm now, but active season has only just begun

Erin would be the fifth and next named storm in the Tropical Atlantic Basin, but is unlikely to form anytime soon.  Even though the beginning of August is commonly referred to as the point in the season when conditions become more active, the forecast for the next ten days is for little or no activity across the “big pond”.  Conditions are unfavorable for tropical cyclone formation through the first week of the month, and only become slightly more favorable during the second week.

Since 1969, tropical storms or hurricanes have formed in nearly all areas of the Tropical Atlantic Basin during the month of August.
August storms typically move into the Caribbean, Gulf of Mexico, or western Atlantic, making all land areas vulnerable.

It’s already been an active season, though, with four named storms in the first two months. The fourth named storm typically doesn’t develop until the third week of August.  Andrea, Barry, Chantal, and Dorian all failed to reach hurricane status, but this is something not unusual for this time of year.  The first hurricane doesn’t develop, on average, until the second week of August.  Climatology is often used to note trends in cyclone formation and enhance forecasts. Over the past 40 years, tropical storm or hurricane formation in August has occurred three times as frequently as in July.  Storms tend to form pretty much anywhere, from the Caribbean or Gulf of Mexico, to several thousand miles out in the Atlantic.  All land areas from Central America to the east coast of the United States are vulnerable to an August storm.


Moisture and instability from the remnants of Dorian are expected to pass very close to South Florida on Friday, before getting pushed back out into the Atlantic over the weekend by an approaching weather system from the north.  Periods of heavy rain and gusty winds will be possible for the southern third of the peninsula Friday and Friday night, tapering off to more typical afternoon thunderstorms Saturday and Sunday.  Rainfall amounts of 1 to 3 inches will be possible, with locally higher amounts in areas of stronger thunderstorms.  Winds could gust to 40 mph in some of the heavier squalls and choppy seas up to 4 feet will be possible just offshore Friday night and early Saturday. The rest of the Caribbean Sea and Gulf of Mexico are void of tropical thunderstorm activity and expected to stay quiet for the next ten days.

Dust storm observed by NASA July 30

Tropical cyclone development is not expected in the Atlantic or Caribbean through the end of the first week of August.  Thereafter, there is only a low chance for cyclone formation in the central Atlantic.  An intense dust storm was observed in West Africa earlier this week, and a large area of this dust has been blown west with the trade winds over much of the big pond.  This dust is filtering sunlight, lowering water temperatures just a bit, and leaving behind a large area of dry air.  It will be nearly impossible for a tropical wave to develop in this environment, much less survive, until the dust is dispersed or moves away.  When this will happen is a bit uncertain, but forecast data suggests the upper-level pattern will be shifting slightly on or around the second week of the month.

July pattern in eastern Atlantic
Forecast pattern by middle of August

For much of July, the Bermuda and Azores high pressure ridge has been unusually strong and displaced a bit to the south.  The faster trade winds on the south side of this ridge have interfered with tropical development so far by mixing and cooling the water, pushing very dry air off the coast of Africa, and suppressing low pressure development.  Long range forecast data indicates this high pressure system will weaken slightly and reform further north by August 10th, thereby relaxing some of the negative conditions for development.  As a result, a few tropical waves would then be able to survive their trip west into the central Atlantic, with even a low chance one of them may develop by the middle of the month.  This shift in the overall pattern is nothing unusual, and is consistent with the trends of climatology that point to a more active month in the Atlantic Basin.

This entry was posted in 10-Day Outlook, 2013 Season, Tropical Weather. Bookmark the permalink.