Issac Forecast Update

Primary threat: Freshwater flooding, heavy rainfall, down tree limbs and power lines, high storm surge east of the Mississippi Delta based on topography

Secondary threat: high wind damage

Lets cut to the chase.

Soon to be Hurricane Issac is taking a very dangerous path towards Louisiana. At the current track it will make landfall right at the Mississippi River Delta. This is farther east than Hurricane Gustav made landfall, and Issac will likely make landfall at a slightly weaker intensity (and slower forward speed) than Gustav. However, the landfall location at this time has made for near optimal storm surge heights for eastern Louisiana and Mississippi due to the storm making landfall almost perpendicular to the coast. The next few figures below show the maximum surge potential for the optimal state, at various strengths. Pay additional attention to those that are specially marked in the captions.

Surge potential for a high end cat 1 (winds 90mph) in between low tide and high tide, with the storm moving onshore at a forward speed of 10mph. *MOST LIKELY SCENARIO***

Surge potential for a high end cat 1 (winds 90mph) at high tide, with the storm moving onshore at a forward speed of 10mph. ***MOST LIKELY SCENARIO***

If the land is covered by something, then it means that either a surge or rain water has predicted these areas will be flooded. I have set the color bar to be the same for all three maps. Even the cat 1 scenario is ugly but this storm looks strikingly familiar to what Gustav did in 2008. Issac makes landfall slightly eastward and puts a 10ft storm surge that is not usually seen for a cat 1 storm, due to the topography. I would look for a blend between the first map and the second map above for potential surge but there is still great uncertainty between now and the landfall. This is because Issac has picked an unfortunately bad storm track, where it will be making landfall almost perpendicular to the eastern Louisiana shoreline. I lowered the forward speed to 10mph at landfall, but Issac will have a threat that Gustav did not have: extremely heavy rainfall along the coast. Lets compare Gustav (2008) and the model output for Issac (2012).

 

Gustav rainfall

Issac's rainfall projections

Issac is interacting with a pre-existing stationary front boundary, which is why high rainfall spreads into Georgia and the Carolinas despite the storm not being anywhere near those locations. This unfortunately slows the storm down to a crawl after landfall. At this time I think rainfall will actually be between 75% and 80% of what is shown above.

And all of today (Monday) where Issac failed to increase its maximum winds but still had a pressure drop produced a wider wind field.

The semicircle near the center of the picture signals that an eye is starting to form. Dry air along the northern quadrant is still interfering with a complete eye from forming

The image above is not a surprise: Issac has struggled to form a complete eye for the past 24 hours due to entrainment of mid level dry air. Issac may still have another 12 hours before it walls off the dry air. Thank goodness the dry air is there or otherwise Issac would already be a cat 2 hurricane. In the very last image of the animation we see an eye emerging.

Model runs for storm path of Issac.

Please be safe if you are along the Gulf Coast.

Update: Winter Prediction

Height anomalies for the next 10 days. Red = warm, blue = cold. Notice the persistent warm anomaly over Southeast Canada (white box) and the resulting cooler weather (blue box). This may be a pattern setting up for the long term. 6/8 winters listed below had this pattern leading into it.

The Pacific Decadal Oscillation failed to switch into a positive phase and is dropping back into a medium negative phase. The warm phase of ENSO has also weakened, but significant upwelling of warmer water will re-energize El Nino conditions. Originally I thought we would be sitting in a very easterly oriented El Nino, but by the time winter rolls around, El Nino will be more oriented towards the central Pacific. The neutral orientation of ENSO will partially offset the negative phase of the PDO. I have pulled several winters that exhibited a medium negative phase PDO and a weak neutral to slightly easterly oriented ENSO. The conditions I have used are unique. I did a 3-month running mean of both the PDO and ENSO, and those winters that had a 3-month running mean of the above conditions were used. Also, 3/5 months out of December - April (April being the wild card) had to meet the appropriate conditions as well (in actuality, Dec - Mar are the critical months).

Winter of 1951 - 1952: 23" of snow
Winter of 1952 - 1953: 22" of snow
Winter of 1953 -1954: 9" of snow
Winter of 1963 - 1964: 76" of snow 
Winter of 1968 - 1969: 84" of snow
Winter of 1978 - 1979: 51" of snow
Winter of 1989 - 1990: 29" of snow
Winter of 2006 - 2007: 16" of snow

63-64, 68-69, and 78-79 have inflated values due to a slight southerly shifted storm track that gave rise to snow from Gulf Low storms instead of rainfall. Despite these inflated values, I am using these years for temperature/precipitation anomalies, but will omit these years for snow observations.

Weather Advance predicted storm track, which I am in agreement with (shift the purple line slightly farther inland up to Cape Hatteras).

So below I have correlation plots of the Multivariate ENSO Index (MEI), Pacific Decadal Oscillation, and Trans-Nino Index compared to precipitation and temperature.

Correlation of Multivariate ENSO Index with precipitation

Long story short, but an El Nino makes it wet for the south and dry for the north.

Correlation of Multivariate ENSO Index with temperature

 Long story short, but an El Nino makes it cool for the south and warm for the north.

Correlation of Pacific Decadal Oscillation with precipitation

 Long story short, but a negative phase PDO makes it wetter west of the Appalachian Mountains and slightly drier east of the Appalachian Mountains. The correlation is lower early/late season, and the greatest impact is going to be west of the Appalachian Mountains.

Correlation of Pacific Decadal Oscillation with temperature

  Long story short, but a negative phase PDO makes it warmer across the Southeast. The correlation is lower early/late season.

Correlation of Trans-Nino Index with precipitation

   Long story short, but an easterly oriented ENSO slightly wetter across the Southeast but drier across the Deep South. The correlation is lower for precipitation and really is only pertinent for January and February.

Correlation of Trans-Nino Index with temperature

   Long story short, but an easterly oriented ENSO slightly warmer across the South and East coast but cooler for the west coast. The correlation is lower for temperature and really is only pertinent for January and February.

Mean of precipitation anomalies for winters most like our upcoming winter

And we put it all together for relevant winters, and we get our precipitation anomalies (in inches) per month for what is projected for this upcoming winter. It will be very wet along the Gulf Coast, Deep South, and Mid-Atlantic, but dry across the Ohio River Valley and the Midwest. An active Alberta Clipper track early on saves the interior of the Northeast early this winter.

Mean of temperature anomalies for winters most like our upcoming winter

And we put it all together for relevant winters, and we get our temperature anomalies (in fahrenheit) per month for what is projected for this upcoming winter. It will be a very quick and cool start for our winter, with an abrupt warming trend in January for the eastern portion of the United States. The Southeast has a cool start and escapes the bulk of the warm temperatures in January. They are just slightly above normal for January. Overall the Southeast will have near normal to slightly above average snowfall for this winter and the Mid Atlantic will have above average snowfall. The Northeast will be warmer the second half of this winter but will see near normal snowfall amounts. Lake Effect snow will be plentiful this year with the active Alberta Clipper Track and an anomalously warm Great Lakes. The upper Midwest sees a large decline of snowfall this winter. The central and southern Rockies and Sierra Nevada see higher snowfall.

I do support a near average to slightly above average snowfall amount for the rest of our state, and above average snowfall for the majority of the Southeast. The Appalachian Mountains straddle the zone between drier/wetter for the Southeast. Higher snow density may cut down total accumulations though, especially with a more active southern storm track. Lake Effect snowfall will be higher especially with the anomalously warm temperatures the lakes already have. High pressure anomaly over southeast Canada may be here for the long haul. My approach got me 33" of snow using a running mean method and a per month method got me 36" of snow for the winter. A lot depends on the wild card and that is the strength of the Polar Vortex