Wednesday, May 30, 2012

TD Beryl poised to soak most of the Triangle

Beryl's circulation and shield of rain strengthened overnight as her center hugs the coast moving NE.  Radar indicates heavy rain and thunderstorms emanating far from center.   It appears that the Triangle, particularly east of Highway 64 is poised for excessive rainfall, 2-4".  In the National Weather Service Radar image below , the banding features on the north side of the center are clearly visible.

Unfortunately the timing of the rain will impact rush hour.  The pre-frontal trough which Beryl is merging is already dumping moderate rain on the Durham area just west of RDU.  This sets the stage for a tough drive to work as rain caused slowdowns will build quickly.  Be patient and safe when driving this morning.

Monday, May 28, 2012

TD Beryl deluging heavy rain on drought stricken areas of the SE

Take notice of the well defined circulation over FL.  TD Beryl is a terrific example of how a hybrid storm that is powered by tropical and baroclinic forces can work mischief over land long after coming ashore. The spiral bands are clearly seen on the below National Weather Service Radar.

Over the next three days the depression will turn NE and dump copious amounts of rain over eastern GA, SC, and NC.  Here in the Raleigh-Durham area we can expect continued bouts of thunderstorms featuring heavy downpours. In this water vapor image the vigorous thunderstorm development in NC is an example of tropical heat and moisture colliding with a baroclinic force, a natural trough east of the mountains which is a frequent summer feature.

Source: Univ of Wisc SSEC

Also in the weather pipeline is an Arctic air mass that will bring a significant shot of cool air to much of the central and eastern US.  I think the computer projections of highs near 80 and lows near 60 are generous.  More on that soon.

Sunday, May 27, 2012

TS Beryl hitting land. Looks like a Hurricane.

The below Radar image courtesy of the National Weather Service looks more like a hurricane than a typical tropical storm.  It will not surprise me if the system is either upgraded or re-classified at a later date 

TS Beryl Update - Near Hurricane Strength

It appears that the improvement in overall structure paid off for Beryl as her top winds are estimated at 70 mph.  The potential for a damaging hit is greatly increased.  If Beryl were to reach hurricane strength she would be only the second hurricane to directly hit Jacksonville since 1871.

Storms like Beryl are interesting to me because even though the storm has tropical structure it is also being fueled by baroclinic features.  In the below water vapor image, I outlined a subtropical jet stream that is feeding the storm from the SW and strong northerly flow that is contributing to the "spin" on the west side of the system.

TS Beryl is a hybrid that is powered by oceanic heat and
baroclinic processes.  She is close to hurricane strength.
Source: Univ of Wisconsin SSEC.

In my experience, storms like Beryl can either have wide ranging impact and maintain strength for a long time or quickly break down as soon as the baroclinic assistance falters.  A baroclinic-tropical system is also called a hybrid storm.   Last summer's destructive Hurricane Irene was an incredible example of a hybrid system.   Despite alleged top winds of 85 mph (Damage near Oriental, NC suggests otherwise), the storm had a central pressure of 952 mb (Cat 4 would be under 950), and a massive storm surge that flooded areas that would have only expected high water in major hurricanes.  The storm also sent 70 mph winds and heavy damage along a belt far from center along I-95 through VA into MD.  Irene caused billions in flood and wind damage as she treked north through the NE US and well into Canada.

The question is: Will Beryl be The Lady or the Tiger?.

TS Beryl taking aim at Jacksonville, FL

It is not uncommon during summers that are transitioning to El NIno or in one to see early season tropical storms. In seasons like the upcoming summer upper level westerly winds in the tropics will either shear off the tops of storms before they can form or turn them away from land.  Therefore what storms do manage to form and threaten land are born much farther north and closer to land.  The good news is that the vast majority of such systems do not tend to be large or powerful.

TS Beryl has improved in size and structure.  Even though her wind speeds are not a cause for great concern, it is likely that when she goes inland a deluge of rain could lead to flooding and gusty winds down some trees and cause damage typical after hours of 30-40 mph winds.  Generally storms which are weak but large in scope tend to hold together for longer periods of time overland.  I am impressed with Beryl's structure.  Note the possible eye-like feature in the visible satellite.

TS Beryl appears to be developing an eye feature.
Source: Univ of Wisconsin SSEC
Even though the storm will ruin Memorial Day for many in FL and GA there is a blessing that can come from the rain that is expected in an area that has become very dry.   Heat ridges, such as the feature that roasted the whole region the past two summers do not tend to hold together over moist land.  The reason is that water vapor is lighter than dry air, therefore sabotaging high pressure development.

June still appears to be the month of summer that will contain the hottest temperatures and much of the remaining tropical storm activity.  Once past June we still appear on track for a moderate summer.

Sunday, May 6, 2012

Summer and Tropical Outlook 2012

Sorry for the prolonged silence. I have been involved in a job transition that has consumed my energy and attention.  Here is my Outlook for this Summer.  It will be shorter and more concise than in the past so please ask questions if more details are needed.

La Nina's effects not going quietly into the night

The ENSO (El Nino-Southern Oscillation) is an Oscillation which has been stuck in a La Nina phase for the past 2 years.   One could argue that some of the foundations of the prolonged La Nina were already in place during the 2009-10 El Nino.  There was the interesting characteristic of a non-El Nino-like excessive rainfall and flooding in northern Australia during that period.

La Nina generates a situation that leads to amplified, blocked weather patterns by the effect on global atmospheric angular momentum (AAM) by the cooling of the waters of the equatorial Pacific.  In general this means that ridges of high pressure dominate east of mountain ranges and land masses and troughs to the west,  The excessive heat of last summer and our recent non-winter were extreme examples of what La Nina can do.

Finally the pendulum is shifting in the El Nino direction but it appears that late Spring and early Summer will contain some lingering blocked weather patterns and hurricane potential.  Therefore, the hottest days of summer appear to be slated for June.  This chart shows the hole that AAM must climb out.  The trend will be our friend as weather patterns evolve into El Nino solutions but it will take some time for the uptrend toward cooler/milder summer weather can take over.

The AAM line is back in La Nina territory
In general there is an uptrend from March lows.
Summer Temperatures

June: The hottest month featuring the warmest days and I completely expect a streak or two of 95+ degree highs.
July:  I would not be surprised if the warmth of June ends in an East Coast or NE Gulf Tropical Storm. Cooler than average to moderate.
August: Near average temperatures with some back and forth as late summer processes attempt and ultimately fail to sustain a prolonged Bermuda High.

If not for some above average Atlantic Ocean temperatures in key regions (+AMO) it would be easy to see summer here in Central NC and VA to be below average.  The Ocean surface temperature variation is also a known Oscillation that is heading toward a negative dominant phase but not there yet.

Tropical Activity

Summers heading into an El Nino tend to not include high numbers/intensity of tropical storms.  Westerly upper level winds in the tropics inhibit storm development.  Overall activity should be below long term averages.

Storm tracks tend to recurve out to sea more quickly than La Nina seasons.  They also form north of the deep tropical regions and closer to land.  We call this "Homebrew" development.  Those storms are often weaker than the Cape Verde type hurricanes but there is far less warning before landfall.

Lingering low AAM is likely to enhance opportunities for early hurricane activity, even the long-tracked Cape Verde type.  Do not be surprised if June features the season's strongest storm.  I am deeply concerned about the NC Coasts, particularly those struggling to recover from 2011 Hurricane Irene.


As AAM rises weather systems will become increasingly progressive.   This means more frontal passages which will increase opportunities for rainfall compared to recent summers.  Watch in June for a crazy hot period that is followed be a tropical storm/hurricane or a prolonged period of heavy tropical sourced rainfall.

Overall, I expect the summer to feature normal to above average precipitation.

Looking Ahead

East Coasr Weather Warriors are salivating at the thought of a weak El Nino during Winter.  It means cold with excessive amounts of snow particularly in areas that are were buried in 2009-10.  If any major  high latitude volcanic eruptions occur in the coming months then the stage would be set for  an expensively cold season.