Sunday, August 30, 2009

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WE'VE ENTERED THE ZONE

SYNOPSIS
The Atlantic basin is entering the historical annual peak of tropical cyclone activity, represented by the two week period on either side of September 10.
Relatively few hurricanes in 2009 may have permitted areas of the western Atlantic and Gulf of Mexico to experience warmer-than-normal sea surface temperatures.
El Nino is present in the equatorial Pacific and expected for duration of the 2009-10 Northern Hemisphere winter.
These and other indicators may signal a snowier winter for the Eastern United States, concurrent with the possibility of an earlier than usual start to the winter storm season.

10:00 AM Sunday, 8-30-09 The Atlantic Basin is nearing the climatological "high water mark" of tropical cyclone activity, historically peaking on September 10. The next two or three weeks may turn out to be the most active period of the entire season. However, a strengthening El Nino signal in the equatorial Pacific may continue influencing westerly shear enough that any developing systems spend more time looking like a threat than turning into one. On the cautionary side, sea surface temperatures (SST) in the Gulf of Mexico are at or above the seasonal peak, with large areas 86 F or greater. All of us coastal-types are not only entering the school zone, but also the hurricane primetime zone. With the 4-year anniversary of Katrina a painful reminder, anything tracking across the Altantic for the next 2-3 weeks bears close monitoring.


For snow-starved powderhounds, the current SST trend is a strong indicator of what dreams may come this winter. I closely monitor Global SST anomalies in the fall as a key signal of what winter may bring. A prime example of this hypothesis is the winter of 2002-03. Hurricane Isabel was the only notable system to significantly affect the East Coast, during a weakening El Nino with Pacific temperature anomalies averaging 1.0 C. Moderate shear influenced by those Pacific anomalies finally relaxed in mid September 2003, permitting Isabel to make her unstoppable westerly beeline for the East Coast. This year, El Nino is stronger, with "sea surface temperatures across the equatorial Pacific .5 to 1.5 C above average," per the Climate Prediction Center's weekly report. The CPC goes on to say, "Current observations and dynamical model forecasts indicate El NiƱo is expected to strengthen and last through Northern Hemisphere winter 2009-10. For snow-starved Mid-Atlantic powderhounds, this could be a very good sign, and a source of my hypothesis.


This hypothesis is centered on two seemingly unrelated events: (1) A strengthening El Nino increases potential for disruptive westerly wind shear in the Altantic basin; and (2) Wind shear that reduces or deflects the impact of tropical cyclones near the coast permits SST's to reach warmer-than-normal levels in certain areas. Undeniable evidence is plain to see in the current Caribbean SST anomaly map as of 8/27/09, as denoted by the "blue swath" indicating the path Hurricane Bill followed in mid-August.


What's the connection to a snowier winter? Just keep reading, we're almost there. But compare the Atlantic SST data to the Gulf of Mexico on that map. Notice that large areas of the Gulf are at or near 86 F (30 C). Whatever energy not removed from the water by tropical activity during summer may persist into winter. That energy can be tapped by developing winter storms crossing the southeast in the much the same manner of the President's Day Storm in February 2003. Although 60 or more days remain for the tropics to "stir things up," with some water temperatures already well-above normal, it will take several strong systems to put a dent in those levels. There are several more factors that must take their place in the "Circle of Life" as it pertains to a snowier signal for this winter, among them trends in the North Atlantic Oscillation, Northern Hemispheric snow cover, Arctic sea ice, and most importantly tracking the snowline descent from Canada each fall. The National Ice Center has links to useful daily imagery.

The long and short of it is this: I hypothesize a high probability winter 2009-10 in the Mid-Atlantic produces at least the climatological "normal" amount of snow (for example, a 30-year average of 19.2 inches at BWI). If the trends continue, perhaps we will see a whole lot more. The real answer that administrators and district-level employees seek is simply: "That's nice for the teachers, but will it be ENOUGH to close schools AND offices? ;-)

Wednesday, August 26, 2009

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ANOTHER WAVY WEEKEND

8:00 am Friday, 8-28-09. Just when you thought it was safe to go back in the water, the Coastal Mid-Atlantic and Northeast for the second time in a 10-day period will face effects from a tropical cyclone. The primary impacts will be another frustrating weekend for beach-goers, boaters and lifeguards alike as Danny's passage will produce high surf conditions and dangerous rip currents. Luckily for coastal residents, this will not resemble the period of late August to early September in 1999, when Hurricane Floyd delivered 12 or more inches of rain on areas still saturated by Hurricane Dennis the week before. Residents of North Carolina can never forget the horrific aftermath of Floyd, with catastrophic flooding that destroyed millions of cattle and ruined thousands of square miles of agricultural land. While Danny is not likely to patch that kind of punch, it is worth noting from a climatological perspective two back-to-back tropical systems taking a similar path along the East Coast. With yet another area of disturbed weather in that critical "Cape Verde" region of coastal Africa, is Mother Nature hinting that Danny and Bill were sent just to lay the red carpet for... Erika?

WHAT WILL DANNY DO? By examining the historical tracking map (paths of previous August tropical storms), and compare that to the current computer model projected paths for Danny as of 7:00 AM Wed, there is comfort in the trends. Both historical data and model output suggest Danny DOES NOT make landfall along the Mid-Atlantic or Northeast unlike Floyd or Isabel (as shown by the StormPulse site). However, it goes without saying that lifeguards, boaters and beach-goers alike face . NOAA reconnaissance aircraft will continue to investigate the storm several times a day, and if the storm reaches Hurricane strength, you'll be among the first to know by monitoring the "Vortex Data Message" on the NHC site.

ON POST FREQUENCY For my colleagues in education, it comes as no surprise that with our return to school in advance of the students, the frequency of posts will be diminished for a time. To bridge the gap and maintain meaningful content, I have a report in development that discusses quantitative data of trends heading into the winter pattern. This post will likely have to wait until Danny has moved on, but in the draft version right now are four key climate indicators which will form the basis of my prediction for the winter storm season.

The four indicators:
(1) Impact of the Solar Minimum on atmospheric temperatures;
(2) Current state of El Nino and effect on North America this winter;
(3) Sea surface temperature anomalies in Gulf of Mexico, western Atlantic and central Pacific;
(4) Evidence of a "negative trend' for the North Atlantic Oscillation (NAO) for fall and early winter.

A majority of this report is written, and it will be presented as soon as time and school preparations permit, but not before the weekend. Until then, we have something new to talk about, so onward with the discussion topics, such as "What will Danny do?" or "Do you remember Floyd?" or "Will this affect the start of school?"

Saturday, August 22, 2009