Will predicted MJO pulse bring chance for first development of the season?

GFS MJO Forecast

GFS MJO Forecast

Even though we had tropical storms Alberto and Beryl already, they were both outside of the hurricane season. Since then, things have been nice and quiet. There are, however, indications that this may change. Let’s take a look at why.

There is an atmospheric phenomenon called the MJO or Madden-Jullian Oscillation that can sometimes lead to increased tropical cyclone formation when it is in its favorable mode. Think of it as a period of fertility in the tropics. A time when rising motion in the atmosphere is more prevalent, allowing deep tropical convection to form. This is what we call the “wet phase” of the MJO pulse and it typically adds a lot more showers and thunderstorms to the tropical regions of the globe where it circulates through.

On the other hand, the “dry phase” is easy to spot due to the sinking motion of the atmosphere, suppressing tropical convection. While development can take place during an MJO dry phase, it’s a lot more common to have development during the wet phase.

There are several computer models, the global models, that predict the MJO pulse and we can track that on various sites. The graphic I have linked to for this blog shows the operational GFS and its ensemble mean- the average of the various other runs of the GFS with slightly different variables. This model, along with others such as the reliable ECMWF, point to an increase in the wet phase of the MJO for the eastern Pacific and eventually the Atlantic Basin. When the MJO is within regions 8 and 1, we should begin to look for an increase in tropical convection. So, going by the graphic, we will need to pay closer attention to the tropics after about the mid part of the month as the wet phase moves through.

You’ll notice first, as it moves through the western Pacific, that we’ll see a typhoon or two develop followed by likely development in the southeast Pacific off the coast of Mexico and Central America. After that time, it is possible that a window of opportunity will open for the western Caribbean. It’s just another piece of the puzzle or a clue that we can use to know when the tropics are perhaps a little more ready for development than at other times. I’ll keep up with it and post more here as we get closer to the predicted date of the favorable MJO pulse.

East Pac and Atlantic Basin trying to get ahead of schedule

The east Pacific hurricane season does not officially begin until May 15 and the Atlantic season not until June 1. However, that does not mean that the tropics will wait until those dates to start producing interesting weather.

Many of the global computer models are hinting at tropical cyclone development in the southeast Pacific and possibly in the western Caribbean over the next week to 10 days. Water temps are warm enough, no question about that. But will upper level winds and other factors such as dry air be pro or con for development? Let’s take a look.

May 10-20 Points of Origin Map (graphic 1)

May 10-20 Points of Origin Map (graphic 1)

First, how about climatology. If we look at the points of origin for tropical cyclones from May 10-20 (graphic 1) we see that both basins have almost the same number of developments 9 for the Pacific, 8 for the Atlantic. So it is possible to see development in both regions during this upcoming time period. This also makes me wonder why the east Pacific starts on May 15 and the Atlantic does not. They both seem to have the same chances for development from this date forward. Interesting, but not for me to decide.

Caribbean Sea Vertical Instability Graph

Caribbean Sea Vertical Instability Graph

Next, let’s look at the vertical instability for the Caribbean right now. Granted this is the current pattern, but it will give us an idea of whether or not the mid-levels of the atmosphere are too dry. As we can see, the vertical instability is currently running just a tad above climatological levels, meaning that the air is nice and buoyant or unstable. This is important because a stable, drier environment, like we saw for almost the entire hurricane season last year in this region, will not allow for tropical cyclone formation or at least keep it weak and disorganized. This is a marked change from last season and something we’ll need to monitor throughout the upcoming season.

GFS 168 Hour 200mb Forecast

GFS 168 Hour 200mb Forecast

Next, upper level winds. The GFS forecasts a fairly nice area of high pressure at the 200mb level in a week. I won’t look beyond a week since too many variables come in to play. But right now, the latest operational run of the GFS shows an area of favorable upper level winds developing over the western Caribbean Sea, extending from the southeast Pacific actually. All we need now is a disturbance of lowering of the surface pressures to set off tropical convection. Will that happen? The various models suggest that it might. I would bet more on the east Pacific than the Caribbean right now, but do not discount entirely the chance of a named storm in the east Pacific followed by the chance of one forming in the western Caribbean Sea before June 1. It’s rare, but it does happen and the region we’ll be watching, according to the climo map in graphic 1, shows that we’re looking in the right place.

So for now, just something to monitor and nothing to be concerned about, not in the least. As things develop, or not, I’ll post more info here and via our Twitter and Facebook pages. Not following us there yet? Click either of the two icons above to join the social media side of HurricaneTrack.

 

Significant non-tropical storm to affect Florida and East Coast over the weekend

It appears that quite a potent storm is going to take shape over the eastern Gulf of Mexico this weekend as upper level energy digs in from the Great Plains. A surface low is forecast to form over the eastern Gulf and bring the potential for very heavy rain and severe weather to portions of Florida (figure 1).

Figure 1: Coastal Storm - 48 Hour Forecast from GFS

Figure 1: Coastal Storm - 48 Hour Forecast from GFS

From there, the low is forecast to move up the East Coast, bringing with it wind and rain all the way to New England. For coastal areas, this will be basically a warm (relatively speaking) Nor’easter. If this were January, we would probably be looking at an epic snowstorm for a good deal of the East Coast. As it stand now, a decent rain event looks to be in store for a wide swath of the Florida peninsula all the way up to Maine with coastal areas experiencing rough seas and a stiff onshore flow (figure 2).

The storm is non-tropical in nature but will tap warm Gulf of Mexico water that is itself running well above normal for this time of year. This warm water will add energy and moisture to the storm system and provide the fuel for it to strengthen and dump copious amounts of rain along its track. If you have outdoor plans this weekend in Florida all the way to New England, keep up to date on the latest weather forecast for your area.

Figure 2: Coastal Storm - 60 Hour Forecast from GFS

Figure 2: Coastal Storm - 60 Hour Forecast from GFS

One excellent tool to understand the impacts better of any storm event is to read the local forecast discussion from your National Weather Service office. You can find this by going to www.weather.gov and typing in your ZIP Code. Then scroll down on the landing page to find “Forecast Discussion”. It will have detailed meteorological information with timing, impacts and projected watch/warning info for any storm event forecast for your area. It’s a great tool, use it.