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Dec 082014
 

The state of ENSO seems very similar to last week’s, with the notable difference that the low-level easterlies have begun to weaken along the Dateline. Check out the comparison below.

Fig. 1 - December 7 TAO

Fig. 1 – December 7 TAO

Fig. 2 - November 30 TAO

Fig. 2 – November 30 TAO

The MJO continues to churn away, with the WH index showing phase 6, although I think it’s best to look at the MJO in its full glory, shown in Fig. 3 below. You’ll notice the active convection over the Maritime Continent, low-level anomalous westerlies reaching almost to the Dateline (forecast to continue eastward) and standard suppressed convection over the Indian Ocean. I suspect these low-level winds are contributing to the aforementioned reduction in easterlies near the Dateline, which seems consistent with a developing El Niño.

Fig. 3 - MJO convection and winds

Fig. 3 – MJO convection and winds

… and I’ll leave it at that since I have a poster to make and papers to grade.

 Posted by at 10:51 am
Dec 052014
 

I couldn’t stop myself from posting about a textbook-looking anticyclonic wavebreak (AWB) in the GFS right now. You can see it in action in the image below, but I encourage everyone to check out the loop, which you can find here to see that there are a number of AWBs in the forecast for the next few days.

Fig. 1 - AWB in the GFS

Fig. 1 – AWB in the GFS. (From Alicia Bentley)

 

Significant AWB over the Atlantic is a known mechanism by which to force the NAO to be positive on synoptic scales. You’ll notice in the figure below that the NAO is, indeed, forecast to remain positive for a while.

Fig. 2 - NAO Forecast from CFS

Fig. 2 – NAO Forecast from CFS

Rossby waves tend to break over the North Pacific and the North Atlantic because that’s where the jets usually end (see Fig.3). They break year-round, but are most common during the Summer when the jets are at their weakest. From a forecasting perspective, the consistent AWB over the North Atlantic is in-line with the CFS forecast of the NAO remaining positive and the polar jet staying fairly strong.

Fig. 3 - AWB Climatology for DJF

Fig. 3 – AWB Climatology for DJF

 Posted by at 4:11 pm
Dec 012014
 

The tropics seem to be awake and active for Cyber Monday. Let’s begin by briefly visiting ENSO… Fig. 1 below shows an update to the SSTs and winds over the central Pacific from the TAO buoy array. You’ll notice that the SSTs are a touch weaker than they were last week (the +1.5°C SST anomaly contour no longer appears). The trades seem fairly robust throughout the basin with little sign of a weakening or reversal. I suspect this will change over the next week or two as a westerly wind burst develops in the WPAC.

Fig. 1 - SSTs and Winds from TAO

Fig. 1 – SSTs and Winds from TAO

 

The hovmöller diagram in Fig. 2 shows OLR anomalies and the CFS forecast (beginning at the horizontal black line). I’ve circled a convectively coupled Kelvin wave and equatorial Rossby wave that are forecast to intersect in the near future. This action is happening within an envelope of active MJO convection, shown in the horizontal map in Fig. 3.
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 Posted by at 1:04 pm