September 2004: A Tale of Two Months?

[donsutherland1]

After some horrible summer forecasting, the August outlook showed some improvement. A more detailed discussion of the August forecast will be provided once all the results are in.

As we head into September, there have been a number of strong signals that could offer insights into the month ahead. Some of the highlights include:

• Excessive tropical activity in August
• A late trend toward a relaxation of the cool pattern that prevailed through much of the summer
• Very warm SSTAs off Atlantic Canada

Given the extraordinary tropical activity, Septembers that follow months similar to August in this area (development of 5 or more named storms, development of 3 or more hurricanes, development of 2 or more major hurricanes in the July-August period, and the landfall of at least one major hurricane) have typically seen the Northeast experience near normal to somewhat above normal temperatures. In the Mid-Atlantic region, temperatures tended to run somewhat below normal to near normal.

Also, it should be noted that if hurricane landfalls continue to be scattered along both the Gulf and Southeast Coasts, this could hold some hints for the coming winter. For now, it remains to be seen how the 2004 hurricane season will end up in terms of landfalling storms.

For those who are interested, in years in which 2 or more major hurricanes made landfall in the United States, New England tended to exhibit a greater likelihood of above normal snowfall. The northern Mid-Atlantic saw a somewhat elevated likelihood of above normal snowfall. The rest of the Mid-Atlantic, including Washington, DC saw equal likelihood of above or much below normal snowfall:

Of the 11 seasons in which two or more major hurricanes made landfall in the U.S., the following held true for Boston, New York City, and Washington, DC:

Boston:
• 50” or more snowfall: 7
• Less than 30” snowfall: 3

New York City:
• 30” or more snowfall: 5
• Less than 20” snowfall: 3

Washington, DC:
• 20” or more snowfall: 3
• Less than 10” snowfall: 3

Of course, it should be noted that far more is involved in identifying analogs for the upcoming winter. At this point in time, this is merely interesting information and not necessarily anything to do with a winter outlook.

Now, back to September:

Based on a review of the evolution of past synoptic patterns similar to the current one and the latest computer guidance and ensemble data, it appears that September will see near normal to somewhat above normal readings in the Washington, DC-Boston region. Precipitation should run somewhat below normal to near normal. There could be somewhat above normal rainfall along or near the immediate coastline and on Long Island, Cape Cod, and Nantucket.

However, it does not appear that perhaps outside of Washington, DC one will need to worry about poet Kathleen Sutton’s description of a heat wave where she wrote:

At the same time, analogs point to the first 10-15 days seeing the greatest warmth, in terms of deviations from normal readings. The last 10 days could close on an unseasonably cool note if some of the analogs bear out.

Given the preponderance of analogs, one might reasonably expect the following:

• Highest temperatures no higher than the lower and middle 80s in Washington, DC through Boston.
• A disproportionate share of 80° or above readings should occur within the first 10 days of September
• Lowest temperatures should fall into the 40s in New York City and Boston. Even Washington, DC has a chance at a monthly minimum temperature under 50°
• The first half of September could see a significant rainfall with widespread amounts in excess of 1”.
• Boston’s mean temperature for September should come in under 66°

Weekly Breakdown for the Washington, DC to Boston Region:

September 1-7: Near normal to somewhat above normal temperatures; Near normal precipitation.
September 8-14: Near normal to above normal temperature; Above normal precipitation.
September 15-21: Near normal temperatures; Below normal to near normal precipitation.
September 22-28: Below normal temperatures; Below normal precipitation.

All-Time Extreme Temperatures for September:

Boston: Highest: 102°, September 7, 1881; Lowest: 34°, September 26, 1879 and September 29, 1914
New York City: Highest: 102°, September 2, 1953; 39° September 30, 1912
Washington, DC: 104°, September 7, 1881; 36°, September 23, 1904

All said, look for near normal to somewhat above normal monthly readings and somewhat below normal to near normal rainfall. The immediate coastal area could see somewhat above normal rainfall.