2013 Steering Pattern / Early indicators

[Riptide]

I almost fell off my seat when I looked at the global sea surface temperature anomaly. Under the impression that this is not record territory but is quite high in comparison to last year. This chart factors in both the Northern and Southern hemisphere but shows a 0.25C+ sea surface temperature anomaly during the peak of the cold season for water temperatures. I suppose this anomaly will drop off again in March as the Southern Hemisphere cools.

[WeatherEmperor]

Luis,

I have a question about the NAO. If there is a negative NAO does that mean more troffs along the east coast and if the NAO is positive does that mean more high pressure ridges near the east coast? This could have implications on whether or not more hurricanes can affect the east coast. What are your thoughts?

Sent from my HTC EVO 4G LTE

[cycloneye]

Luis,

I have a question about the NAO. If there is a negative NAO does that mean more troffs along the east coast and if the NAO is positive does that mean more high pressure ridges near the east coast? This could have implications on whether or not more hurricanes can affect the east coast. What are your thoughts?

Sent from my HTC EVO 4G LTE

Hi my friend. Negative NAO implies less trade winds which first cause the sst's to warm and second depending on where the Bermuda high sets shop may cause systems to recurve and not threat the East Coast of U.S. We have to see if an East Coast trough develops or high pressure establishes to know then about landfalls.Positive NAO implies potential Caribbean Cruisers that may go to Central America or GOM depending if the ridge is strong or not. I hope that I explained in a simple way about this as I know that there are more factors that can be important as the NAO and that is why maybe a Pro Met can explain better than me about the AMO,AO,PDO,PNA etc,etc,etc ------.

[Hurricaneman]

Atlantic Basin instability February 22 2013

GOM: average -11 current -9 which is 2 above normal instability

Carribean: average 0 current -2 which is 2 below normal instability

East Coast: average -12 current -16 which is 4 below normal instability

Tropical Atlantic: average -7 current -10 which is 3 below normal instability

SubTrop Atlantic: average -9 current -7 which is 2 above normal instability

the overall numbers of the whole atlantic basin is -5 below normal and is 4 higher compared to February 20th to normal

also why did the normal climatology instability drop like 5 from the previous update, could that higher number that it had for its climatology number a few days ago have been an error because the climatology numbers now charted equate to last years charts

[cycloneye]

As we know the NAO is one of the important factors to watch how it evolves. The models keep the NAO in negative for a while. This may have implications on the sst's and the steering. Let's continue to watch how this factor continues to evolve in the next few weeks.

GFS



ECMWF

[TropicalAnalystwx13]

Luis,

I have a question about the NAO. If there is a negative NAO does that mean more troffs along the east coast and if the NAO is positive does that mean more high pressure ridges near the east coast? This could have implications on whether or not more hurricanes can affect the east coast. What are your thoughts?

Sent from my HTC EVO 4G LTE

Hi my friend. Negative NAO implies less trade winds which first cause the sst's to warm and second depending on where the Bermuda high sets shop may cause systems to recurve and not threat the East Coast of U.S. We have to see if an East Coast trough develops or high pressure establishes to know then about landfalls.Positive NAO implies potential Caribbean Cruisers that may go to Central America or GOM depending if the ridge is strong or not. I hope that I explained in a simple way about this as I know that there are more factors that can be important as the NAO and that is why maybe a Pro Met can explain better than me about the AMO,AO,PDO,PNA etc,etc,etc ------.

A negative NAO signature is actually worse for the United States and Caribbean than a positive NAO. The Bermuda high may be weaker, yes, but that does not mean it's non-existent. The high is more spread out across the central and western USA, directing systems towards Central America and especially the lower 48. Many of our worst hurricane hits have come from a negative NAO.

...of course it still depends on the setup. Troughing over the East, negative NAO or positive NAO, will more than likely direct systems out to sea.

[wxman57]

...snip...

also why did the normal climatology instability drop like 5 from the previous update, could that higher number that it had for its climatology number a few days ago have been an error because the climatology numbers now charted equate to last years charts

From Andrea Schumacher at Colorado State:

Last fall, NESDIS replaced the TCFP with a global version. In doing so, the sub-basin boundaries changed slightly in order to accommodate the larger domain, which in turn has changed the sub-basin averages. I see how this can make year-to-year comparisons tricky.

What she's saying is that the basin boundaries changed and now there's a new climo line for each basin. The new lines can be a good bit different from last year. So you cannot compare the current instability to any of last year's graphics.

[Hurricaneman]

Atlantic Basin instability March 5 2013

GOM: Average -10 Current -15 which is 5 below normal instablility

Carribean: Average 0 Current -2 which is 2 below normal instability

East Coast: Average -11 Current -17 which is 6 below normal instability

Tropical Atlantic: Average -7 Current -10 which is 3 below normal instability

Subtrop Atlantic: Average -9 Current -8 which is 1 above normal instability

So overall instability below average is 15 which if it continues could be very prohibitive to tropical development except for maybe the subtropical atlantic

[tolakram]

Tropical Atlantic instability remains below normal and falling.

[Riptide]

Good post from TropicalAnalystwx13

Looks like another active season...

- Negative NAO is currently in place, and is forecast to remain so throughout the period. For those that happen to not know, a negative NAO reduces the strength of the area of high pressure that is typically situated across the north-central Atlantic. A weaker-than-average high pressure causes weaker-than-normal trade winds across the Caribbean and remainder of the hurricane hot spots. This allows for less evaporational cooling and allows sea surface temperatures to warm quite dramatically. We've seen this already in the past two weeks.

- SSTs in the equatorial Pacific are currently in the Neutral phase. It's been quite interesting, really, watching the anomalies switch up and down for the past month. Most models show a basic stalemate through the rest of the Spring and into Summer, but the CFSv2 (not really reliable though) shows an El Niño. A potent el niño would probably be hard-pressed to get anyways given the negative PDO signature that has persisted for many years now.

- The Atlantic tripole is returning. This is an area of warm waters are the eastern/central Atlantic, cool waters around Newfoundland's latitude, and then warmer waters north of that again. A signature like this focuses the MJO in the Atlantic due to increasing lift.

Something we will have to watch out for this season is how vertical instability and the Gulf of Guinea play out. Instability is generally normal at this time acoss much of the western/central Atlantic, but horribly below average across the eastern Atlantic. I realize it's typical for this time of the year, but seriously, it's bad. The Gulf of Guinea remains warm, which isn't necessarily a bad thing, but cooler waters in that region would support a farther north ITCZ and more robust tropical waves. I should note that 2011 and 2012 were cool Gulf of Guinea years and 2010 was a warm Gulf of Guinea year; all three featured 19 tropical storms.

What's you guys' thoughts? My very early guess would be 15-19 tropical storms. I'm not comfortable with the strength of these because it definitely hinges on vertical instability.

[TropicalAnalystwx13]

Tropical Atlantic instability remains below normal and falling.

As is expected for this time of the year with stable air across much of the basin.

[tolakram]

You keep saying below normal is normal. I'm not exactly sure what you mean. If it's expected, or normal, then the black average line should show it, and it does, but current values, in blue, are below that.

[Riptide]

You keep saying below normal is normal. I'm not exactly sure what you mean. If it's expected, or normal, then the black average line should show it, and it does, but current values, in blue, are below that.

It's worth noting that instability values were above average during this time in 2011. More than likely it does not have any significance in predicting future instability. The deviation from normal is not that large, could just be natural background variations.

2011 Tropical Atlantic Instability

[cycloneye]

Another thing to watch in the comming months is how the rainfall is in the Sahel region. Is early but we can have an idea of how West Africa is doing in terms of rainfall.



http://www.cpc.ncep.noaa.gov/products/a ... rica.shtml

[cycloneye]

My take on the instability in the Tropical Atlantic is that is doesn't matter at this time of year but starting in mid-May it starts to be a factor.In 2005, instability was below normal until the start of the season and we know how that season turned out to be. An equatorial ridge axis is over the MDR at this time of year and because of that,you can expect stable conditions with that kind of setting.

[TropicalAnalystwx13]

You keep saying below normal is normal. I'm not exactly sure what you mean. If it's expected, or normal, then the black average line should show it, and it does, but current values, in blue, are below that.

We hardly ever see vertical instability values follow even the average for this time of the year because of the ridge of high pressure located in the east-central Atlantic that induces stable air across much of the region.

[wxman57]

Very significant difference in the March European forecast of mean sea level pressure anomaly across the Atlantic Basin vs. March of 2012. Last year, the Euro was forecasting very high pressures across the deep tropics (and most storms formed in the subtropics). This year, pressures are forecast to be nearly normal. That would suggest a greater risk of major activity in the Caribbean/Gulf.

Forecast from March of 2012 for July-September:


Forecast from March of This Year:

[cycloneye]

Very significant difference in the March European forecast of mean sea level pressure anomaly across the Atlantic Basin vs. March of 2012. Last year, the Euro was forecasting very high pressures across the deep tropics (and most storms formed in the subtropics). This year, pressures are forecast to be nearly normal. That would suggest a greater risk of major activity in the Caribbean/Gulf.

Forecast from March of 2012 for July-September:
http://home.comcast.net/~cgh57/2012.gif

Forecast from March of This Year:
http://home.comcast.net/~cgh57/2013.gif

The site that I have of the MSLP by ECMWF still does not have the March update.
http://www.ecmwf.int/products/forecasts ... 0summary!/

From what site you got the March update?

[wxman57]

That's where I got it, Luis (slightly different path):

http://www.ecmwf.int/products/forecasts ... 0summary!/

[TropicalAnalystwx13]

Very significant difference in the March European forecast of mean sea level pressure anomaly across the Atlantic Basin vs. March of 2012. Last year, the Euro was forecasting very high pressures across the deep tropics (and most storms formed in the subtropics). This year, pressures are forecast to be nearly normal. That would suggest a greater risk of major activity in the Caribbean/Gulf.

Forecast from March of 2012 for July-September:
http://home.comcast.net/~cgh57/2012.gif

Forecast from March of This Year:
http://home.comcast.net/~cgh57/2013.gif

This month's looks a bit more reasonable than what the February one showed for the same time period, though I'd imagine it's still a little too bullish on MSLPs given the current setup.