ECMWF Winter Forecast Looking Good for East Coast

ECMWF Winter Temperature Map
Interpretation by Brett Anderson of Accuweather

ECMWF Winter Precipitation Map
Interpretation by Brett Anderson of Accuweather

The latest ECMWF appears to be showing a scenario typical of El Nino conditions over the upcoming winter, with above normal precipitation over parts of the Gulf Coast and dry conditions over the Northwest.

Brett Anderson of Accuweather writes posts for Canadian weather, but also releases maps of the ECMWF model from time to time. Due to the ECMWF's strict policy of releasing maps, the only legal way to display the seasonal ECMWF forecasts is by 'interpretations' such as his shown above.

The ECMWF is projecting a high latitude blocking pattern setting up, shown by a notable warmer than normal airmass settling in over areas close to Greenland as well as above normal temperatures in Alaska. The Alaskan warmth indicates a ridge in the Gulf of Alaska may be present. This ridge can incite cooler weather to flow into the US, and was not present last year when heat dominated the winter.
Additionally, warmth near Greenland enhances the possibility of a continuation of the negative NAO that has been seen recently. While it is not a sure sign of a negative NAO, the chances based on this warmth appear to be enhanced.

Precipitation-wise, an El Nino signal of a dry Northwest and wet Gulf Coast are present, but not a wet East Coast. In fact, this forecast indicates that a portion of the Northeast may actually end up slightly drier than normal. While the rest of the model does seem fairly trustworthy, this part does not seem right to me. A moderate El Nino appears likely this winter, and this, combined with a favorable NAO and stratospheric conditions, would make for a snowy Northeast.

It will all become much clearer with time, but for now there remains a few pieces of the puzzle that don't fit quite right.

You can read Brett Anderson's blog and ECMWF posts by clicking here.

Andrew

Ernesto Dissipates; Redevelopment in East Pacific Likely

Tropical Storm Ernesto dissipated today as it encountered landfall in Mexico, but as it emerges into the open waters of the East Pacific, redevelopment appears likely.

The NHC has outlined this system with a 60% chance of redevelopment into a tropical cyclone. There will be some obstacles in the way, however, with shearing already above 30 knots in Ernesto's path and upper level divergence at a pretty high value. Despite this, the system is maintaining a good form by satellite standards, and it would only take additional convection and strengthening to get the system where it needs to go.

The SHIPS forecasting model has it reaching above 100 knots of wind speed, as seen below.

                TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 20 17 16 16 19 30 43 56 67 78 90 100 106

Note: 'No Land' refers to the strength it can reach with no land interaction.

Andrew

Tropical Depression SEVEN Forms

(Refer to my last post on where I think the track will go)

The National Hurricane Center is forecasting Tropical Depression SEVEN to move to the west and eventually northwest along the Caribbean. This goes in line with my estimate on where this system could go. The link to that post is above.

If I were to look extremely long range, I would think that there is a fair chance of entering the Gulf of Mexico. However, this could be another 'Ernesto', and we all know how that turned out when the Gulf appeared at risk.

Andrew

Caribbean May Be At Risk Over Invest 92

I believe that model guidance may be incorrect in assumptions that Invest 92 will be a threat to the East Coast and skirt the Virgin Islands to the north, as the steering layer chart above differs from the model guidance.

Steering charts are used for storms within a certain boundary of strength. This one is used for systems with central pressures at or above 1000mb, so we will use this chart to determine where Invest 92 will go. While it is not clearly defined, one can find it in the warm colors below the massive ridge in the Atlantic Ocean.

Looking at this steering chart, the models have good reason to be confused on the track- it is just below the ridge of high pressure. If it were to be influenced by this ridge, as many models are saying, the system would keep straight west and fire off towards the East Coast.
However, as a few models are starting to trend to, there is a tight belt of winds just below the ridge that would take the system southwest, through the Caribbean and possibly towards the USA. I find this to be more possible, as the warmest colors are in the belt of higher winds, and thus would have more influence on where the storm goes. Additionally, this is where the NHC indicates the system is, as shown below on the most recent NHC chart. Invest 92 is the one circled in red.

Andrew

Disturbance Moving Off Africa May Pose Caribbean Threat

A disturbance is moving off Africa this morning that may eventually produce a threat to the Caribbean islands.

This disturbance is located in the middle of the 10 (degree) north line. Its appearance is disorganized, with the main cluster of showers and storms already offshore and mainly debris clouds in tow. Despite the disorganization, I see a potential tropical system on our hands, and here's why.

Because this system is at the 10 degree north line, I find it reasonable that, should movement continue west, climatologically the system would want to enter the Caribbean in a similar way in which Hurricane Ernesto did.

This steering layer wind map represents possible motions for storm systems with central pressures at or above 1000 mb. According to this map, the disturbance would likely continue to move westward and encounter a possible southward motion in the process, However, should this current pattern hold, an eventual westerly-turning-northwest movement would likely result.
Another possibility is that the system is pushed north and is thrown into the massive high pressure system holding an iron grip over mich of the Atlantic. This high pressure system would either result in an East Coast threat or throwing the disturbance out to sea.

But, even if it moves west towards the Caribbean, will it survive the trip?

This map shows shear tendencies over the Atlantic. At the moment, we have generally light shearing over the area where this disturbance would travel should it move west. This would prove beneficial for additional development. There is an area of about 30 knots of shearing on te lower right-hand corner of the image, which i where the system may run into some trouble. However, should it survive that bout, and low shearing holds up over the 10 degree north line, I believe additional development for the disturbance is likely.

Disclaimer: This is long range, and tropical systems are known to be notorious for long range forecasts. This is based off of what I believe may happen, but is not to be taken seriously until the system is a few days away due to the trickiness that comes with tropical forecasting. If it comes down to it, heed warnings from the National Hurricane Center and not from here at The Weather Centre.

Andrew