Its been a long time coming for one of these blogs. I figured this lazy Sunday will be the best time to write one. The blog is going to look at key differences in our Sea Surface Temperature Anomalies (SSTA) between August and September, and it will also look at the rapid changes our upper air pattern (500mb level) is going to go through as we head into October.
A lot has been made about the upcoming El Nino event.
- Will it be moderate, strong, or super?
- Will it be basin-wide or east-based?
- Will it reach a plateau then start weakening through the winter?
These are just some of the many questions people are asking. Personally, I have made it a point in the past to not try to figure these things out too early in the season. What the Nino looks like now could look completely different in November. There are many reasons for that. The main one being it's difficult to forecast where the best forcing takes place (how the MJO behaves) along the Equatorial Pacific.
The SSTA graphic above is for the month of August. Over the month, we saw rapid strengthening in Nino 1+2 region (eastern most based region of the ENSO) and continued warmth in the northern Pac. Lets see if these trends have held to this point.
Nino Region 1+2 continues to maintain the core of the warmth. While Nino Region 3.4 has warmed slightly...its been a very slow and seemingly difficult process. Also, check out the area of water in the GOA to the NW Pac of the U.S. It looks like it has cooled some, right?
Take a look at the September (to date) H5 map above. The ridge has been pushed back west allowing for more of a neutral to positive EPO. This has brought cooler weather - or negative H5 heights - to that region.
The 7-day change in SSTA shows that area of the Pacific continuing to cool. Obviously this it not ideal to see because it could lessen the probability of seeing another winter with a mean -EPO. A
-EPO these last couple of winters forced, or displaced, the polar air in the Arctic to the eastern CONUS. Then again, with a strong El Nino event currently taking place it is difficult to find analogs that had a ++ENSO with a persistent -EPO over an entire season. We will see if this trend continues into October...but I have a feeling it will not.
The upper air pattern is going to undergo significant changes this week.
The beginning of the week is going to feature much of the same weather we have seen the last couple of weeks - zonal flow with temps in the upper 70's to low 80's. Negative heights persist across central/northern Canada and the Southeast US, while positive heights drape through most of the U.S. and eastern Canada. Refer to the September H5 map above to see how incredibly warm east-southeast Canada has been this month.
Check out where our pattern is headed by the 1st weekend of October. Canada has gone from experiencing negative heights to way above normal heights. The EPO region (Alaska / GOA / NE PAC) is also expected to see a ride resurgence take place. This "blocking" pattern is going to have big effects on our weather here in the northeast.
- We will enter a normal to below normal temp regime
- There will be greater rain chances going forward - at times - significant rain
We could see our first significant rain threat of the season by the end of this week or weekend. With abrupt heights changes from negative to positive across Alaska to Canada, waves of vorticity that drop down from Canada will not be able to move much. There will be a lot of vort interaction. This is going to cut-off our flow and potentially bring nasty weather to our area. The H5 map above is an example of what the models are trying to do for next weekend. H5 closes off over the Midwest and an area of low pressure forms off the coast.
EURO (left) and GGEM (right) are both insisting on a potent rain event next weekend. There are differences in track and storm intensity at this moment. We will have a clearer picture of how this storm envelops by Tuesday.
Moral of the story:
- El Nino needs to begin looking more like a basin-wide event rather than east-based
- Cooling SSTA in the North Pac may not last after this pattern change
- Sustained Fall-like weather will begin the end of this week
- Potent coastal rain storm likely the end of this week (at least 1" of rain expected)
- Rain chances should last through much of October
I hope everyone has a fantastic Sunday.
Best,
Francesco
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