Activity in the East Pacific, continued quiet in the Atlantic.

June 20, 2009

Thursday saw the formation of the first tropical depression in the Eastern Pacific. The system did not strenthen much further before making landfall and dissipating in Mexico, yesterday.

Because of that, we have yet to see a tropical storm in either the Atlantic or eastern Pacific.  This is not unusual for the Atlantic, but is for the Pacific.  Normally we would already have a named storm in the books and be talking about the second one by the last week of June.

The answer to the  question of the latest forming first tropical storm in the North Pacific is somewhat muddled by the varying quality of the history book.  The records are nearly unaminously considered to be spotty prior to satellite coverage in 1966.  However, many use 1971 as the starting point for reliable records, due to the lack of consistent quality satellite images and intensity estimates that were rough guesses (note the number of “45 knot” tropical storms and “75 knot” hurricanes in 1968, for example).   If we uses 1971-present as the benchmark, then we are in record territory as the latest first storm during that period was 1994’s Aletta, which formed on June 18 (local time).  However, if we were to use 1966 as the starting point, then we are not close to the record, because the first named storm of 1969, Ava, did not form until July 2.

Record or not, it is still unusual to be this far into the season without a tropical storm in the Pacific, but there are existing opportunities for that drought to come to an end.  There’s a reasonable chance of a depression forming off the west coast of Mexico in the next day or two. If it were to do so, it would have more time, if not necessarily better conditions, to become a tropical storm than the first tropical depression did.   A more outside chance exists near the western edge of the basin where there is a broad area of low pressure with thunderstorm activity.  The most recent Tropical Weather Outlook assigns it a low chance of tropical cyclone formation (compared to medium for the other system).

First tropical storm of the season in the making?
First tropical storm of the season in the making?

No such prospects exists in the Atlantic at this time.  The scenario of  a tropical cyclone forming in the western Caribbean mentioned in my previous post failed to materialize.  There aren’t even any marginal possibilities for the next few days.

This quiet of course, is not atypical as the average date for the first Atlantic tropical storm falls in early July.  Looking over the 1944-2008 seasons, it is roughly a 50/50 as to whether we have a tropical storm before July 1st or after.  If we don’t have one by July 1st, it is again a 50/50 as to whether one forms by August 1st.

A relatively tranquil Atlantic

A relatively tranquil Atlantic

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