US Weather Commentary

The Atlantic Basin continues to be immersed in a very conducive atmospheric [MJO] phase that will likely persist for several more days.  While other variables are obviously necessary for storm formation, the impact of the MJO on the Western Hemisphere has been starkly evident in the formation of 6 Tropical Depressions (including 2 Tropical Storms and 2 Hurricanes) in less than 3 weeks across the East Pacific.

We perennially give the analogy that tropical storms are like water balloons in a swimming pool, and unclassified/disorganized Waves & Disturbances can be even more capricious.  Thus, it's best to: ignore model output beyond 7 days, stay clear of models that don't specialize in tropical physics (i.e. avoid the popular models referenced in U.S. temperature forecasting), and realize that Tropical entities can alter, shape and create their own environment (ridges, steering, flow, etc.) each and every day.

As you know, our research has detected an evolution over the past 15 years of the Inter-Tropical Convergence Zone [ITCZ] shifting further southward toward the Equator.  This has increased the frequency of storms forming or passing south of 12°N Latitude, with this latest Wave one such candidate.  Should Tropical Depression #3/CRISTOBAL form, steering currents should take it towards the Lesser Antilles/Caribbean over the next few days.  Even a passage North of the Greater Antilles (i.e. Puerto Rico, Hispañola) does not place North America out of the woods, so it's way too early in the game to close the book or open the book of long-term prospects on a Wave that has yet to be classified.

Tropics References  and Further Reading:

* The average date that the "B" Storm forms in the Atlantic is July 28th, and the average date that the "C" Storm forms in Atlantic is August 11th. So we're only in the 1st inning of the Hurricane Season, and already well ahead of climatological pace.

* Remember that the NHC has a disproportionate tendency to classify tropical storms on either Weekday Evenings (5 PM ET - 5 AM ET), Holidays, or over Weekends. They are also usually quicker to pull the trigger on classifying a system close to land/North America than they are for a system far out in the Atlantic.

Heat Event #4 to impact East-Half of U.S. & I-95 corridor this week........

The consistent heat drummer of Eastern Texas plays on with Dallas soaring to its hottest temperature yet this Summer of 102°F on Saturday, and sustaining its streak of every day this July breaking 97°F.  Houston re-joined the 95+ club with back-to-back 98°F readings, and as typical this Summer, an arc of heat will expand or transfer over to the Eastern & Northern States in the coming days.

Subsequent heat events across the populated I-95 corridor have ranged from dramatic to stealthy & muggy, and models have done a poor job in anticipating the spike magnitude of the former, as well as underestimating the 7-Day CDD totals of the latter  [please see 2008 in historical perspective, below].  Correspondingly, those who solely relied on model output or short-term forecasts from last week, might be surprised to learn that this rumored "tame week" will actually produce a sizable stretch of 90°F days starting Wednesday with some mid-90's thresholds being eclipsed for Washington D.C., Baltimore, Philadelphia and possibly New York.

While Heat Waves often "sneak up" on models, recent medium-range model output was especially erroneous & haphazard due to the mishandling of both Bertha's physics as well as upstream physics. The Polar Vortex was sinking much further South over Alaska which through a series of atmospheric fulcrums, lifted up the Eastern North America storm track.  This had the double consequence of: [1.] Only allowing (yet again) Mid-West troughing to briefly skim the Northeast (July 1st was the only Below Normal Day for D.C. and New York has only had 2 such cool days); and [2.] Left Bertha in a very weak steering environment (hence her stalling & meandering), allowing her to pump up Eastern Ridging for that many more days.

Our fluid dynamic calculations from last week were finally represented at least qualitatively by model output when Hurricane Recon over the weekend provided some sampling of the West Atlantic environment, yielding some insight as to the temperature consequences of this "Atmospheric Traffic Jam".

Summer 2008 in historical perspective.....

While every Season is as unique as a snowflake, the only years in recent history that even come close to doing cumulative justice to the historic warm East Coast Summer of 2008 [June-August], are a blend of 2005 [cool May followed by 2nd hottest Summer in NYC history] + 1999 [I-95 heat spike events].  The following is a running summary of Summer-to-date Cooling Degree Days for key East Coast hubs which our research believed cumulative Heat Anomalies would be mainly focused this Summer, for your ongoing reference:

Summer CDD* Totals (through July 13th):

Location:               1999+2005:    2008:

Boston                     298                323
New York City          459             508
Philadelphia             450             519
Washington D.C.      528             587
Richmond                 481            593
Raleigh                     534            649

* Official NCDC integer format CDD.

"Give me a month with 9 Below Normal Days, and I'll show you one of the hottest Summer months in History." - Cornell University Climatologist