Hurricane Irma is coming – I just don’t know where it’s going

A lot of people have asked about our app – it is called Hurricane Impact and is available on the iPhone App Store. Search Hurricane Impact

8 AM ET September 2, 2017

I am back home in North Carolina after a 10-day saga in Texas dealing with hurricane Harvey. That story is still very much ongoing, obviously, as the early stages of clean-up and recovery begin. The Harvey field mission was very successful with wind and pressure data being collected in Corpus Christi and several unmanned camera systems being deployed during both the hurricane impact and the flood impact.

Now it is time to focus on Irma.

Hurricane Irma five day forecast points plotted over upper ocean heat content map. The future track takes Irma over increasing sea surface temps as well as increasing upper ocean heat content - which will result in significant intensification.

Hurricane Irma five day forecast points plotted over upper ocean heat content map. The future track takes Irma over increasing sea surface temps as well as increasing upper ocean heat content – which will result in significant intensification. Click on image for full size.

Right now, the hurricane is fluctuating between category two and category three intensity as it moves over water temps that are just warm enough to sustain the heat engine. In a couple of days, the water temps will increase quite a bit, providing more fuel for a much stronger version of Irma than we see now. Fortunately, it will still be far away from any land areas.

The first region to consider for potential impacts, either direct or indirect, will be the Leeward Islands, especially the northern Leewards.

So far, the official forecast track from the NHC keeps the core of Irma to the north of all of the northern islands and presumably Puerto Rico. However, it is too soon to know if this will verify or not. The ECMWF model is fairly close to the islands while the GFS is notably farther to the north as Irma passes by. We are going to need another 48 hours or so to work out the details of this portion of the track for the hurricane and in my opinion, the west-southwest dip that is forecast will be the key here. The longer Irma remains at the latitude of the islands when the high pressure to its north eases up and allows the hurricane to gain more latitude, the greater the risk for a direct hit. Interests from Dominica to Puerto Rico should be paying very close attention to Irma over the next few days. In this case, timing will be everything – the later that turn back out of the WSW dive the more the risk increases.

After the next five days, the focus will shift to the Bahamas and the Southeast coast, including Florida. This part of the future track of Irma remains very uncertain. Both of the major global models, the GFS and the ECMWF, suggest a possible threat to the region in about a week to ten days. Here too, it will be all about timing and position.

As Irma moves westward, steered by a strong Bermuda High, a trough of lower pressure in the atmosphere will dig in to the nation’s mid-section, bringing a wonderful shot of fall weather to a good deal of the eastern U.S.

This trough will push on and erode the western portion of the Bermuda High. This will allow Irma to gain latitude once again – presumably. It all depends on how far north Irma is once the trough digs in. A more northerly and faster west track would place Irma closer to the weakness that the trough will create – allowing for a chance to turn north and then maybe northeast and out to sea.

On the other hand, if Irma if farther south and east, the trough digs in, then lifts out a few days later, allowing the Bermuda High to build back in – sending Irma on a NW track towards the Southeast. There are multiple variations of this scenario but the overall idea is, in my opinion, going to come down to how far west and north Irma is when the trough begins to lift out.

Since we are talking about at least seven days from now, it is impossible to know what will happen. For this reason, everyone from the Bahamas to Florida to the Canadian Maritimes should be keeping tabs on Irma every day. There’s no reason to worry just yet in any particular location. Right now, as I am doing with my family, just add a little more to your supplies each time you visit the store. An extra gallon or two of water, maybe have your generator checked if you’ve used it anytime in the past. Do these small things now before the stress and anxiety ramps up next week – which it very well might for some people.

We have time right now to watch and react at a steady pace. Maybe it will be ok and Irma will turn out to sea. If not, luck favors the prepared and my advice is: start preparing a little more each day from here going forward. You just might need it.

I will have a video discussion posted later this afternoon which will go over the latest from both the GFS and the ECMWF.

M. Sudduth

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If GFS is right, we are in for a busy week

On Friday, I wrote about the possibility of the season’s first hurricane developing from a tropical wave that was about to emerge from the coast of Africa. At that point, two of the major global computer models, the GFS and ECMWF, were both indicating the development of the tropical wave as it approached the Lesser Antilles.

Now, here we are on Monday and the GFS essentially stands alone. The ECMWF has all but completely dropped the notion of development while the GFS is about as consistent as it can be.

If we follow the evidence we can try to figure out what may end up happening – while also either confirming or denying the GFS and its ability to forecast the development of a tropical storm in the deep tropics.

I have prepared a video discussion covering this intriguing situation by taking a close look at not only the model forecast but also what we see in front of us right now. What does the evidence show? Is there enough there to support the idea of a tropical storm forming later this week? Check out the video below to learn more.

M. Sudduth July 10, 2017

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Models hinting at possible first hurricane of 2017 season

Graphic from Colorado State University's July hurricane season forecast outlook showing the below avg wind shear (blue color) across the MDR for the month of June.

Graphic from Colorado State University’s July hurricane season forecast outlook showing the below avg wind shear (blue color) across the MDR for the month of June. Click for full size.

The update from Colorado State University to the 2017 Atlantic hurricane season forecast made mention of the fact that, during the month of June, sea-level pressures were well below average across the deep tropics – also known as the MDR or Main Development Region. This is the area between Africa and the Lesser Antilles and has seen its share of powerful hurricanes over the decades.

In recent years, however, the MDR has been notably quiet. Dry air, strong upper level winds and generally higher than normal pressures have kept the region much more benign – resulting in far less hurricanes such as what we saw in 2004 with Frances and Ivan, as examples.

This year, it is becoming more and more obvious that the sleeping giant is awakening, so to speak. Water temps across the MDR are above normal, wind shear is below normal and surface pressures are below normal. The result thus far has been the formation of tropical storm Bret last month (extremely rare to have MDR tropical storms in June) and now, most recently, tropical depression four – technically a tropical cyclone though below tropical storm intensity. The only significant mitigating factor keeping TD4 in check has been a large Saharan Air Layer or SAL event that has pushed ample dry air in to the deep tropics, smothering the depression and keeping it from strengthening further. This SAL outbreak is typical for July, having a tropical depression in the MDR is not.

ECMWF model at day 5 from last night's run showing energy or vorticity at the 850mb level of the atmopshere (circled in green). Image courtesy of Levi Cowan - tropicaltidbits.com

ECMWF model at day 5 from last night’s run showing energy or vorticity at the 850mb level of the atmosphere (circled in green). Image courtesy of Levi Cowan – tropicaltidbits.com. Click for full size image.

Now comes the next chapter in this story. Both the GFS and the ECMWF are now indicating the development of a tropical storm originating from a tropical wave that is about to emerge from the African coastline. I want to be clear, the development happens beyond the 5-day time frame but well within the next 10 days. Since both of these global models now indicate this happening, it has my attention. In fact, both models go on to develop the system in to what would likely be a hurricane later on in their forecast periods but again, not at some ridiculous time frame such as 10 to 14 days out – what many consider to be “model fantasyland”.

What concerns me about this is the mere fact that it is still early July, several weeks ahead of the traditional beginning to the normal run-up to the peak of the season and we’re talking about yet another MDR system trying to develop. In other words, if it’s this busy now, when climatology says it should not be, how busy will it be when the natural background state is inherently favorable? That usually sets in around August 15-20 and lasts until the end of October.

I make it a point to refrain from being an alarmist – those who have followed my blogs and video discussions know this and I stand firm behind that belief. At this point, I am beginning to worry that this season could end up exceeding all of our expectations in a bad way. The time-tested saying of “it only takes one” remains intact but this is the kind of season where we could be looking at multiple “it only takes one” events. Please keep in mind too that I am not talking about just the United States in terms of impact. The Lesser Antilles are front and center for any action that rolls out of the MDR and west of there we have Puerto Rico, Hispaniola and Cuba. This is the kind of season that could affect a lot of people across the Atlantic Basin and in areas that can least afford such bad luck.

I am going to say it, the signs are ominous right now. We’ve gone a long time without experiencing a category three or higher hurricane in the United States. They’ve also been somewhat rare elsewhere with the exception of Matthew and its devastating impacts on Haiti, eastern Cuba and the Bahamas last year (Joaquin in 2015 also impacted portions of the Bahamas). It is time to take notice and be ready to act.

Needless to say I am going to be watching the evolution of this next potential system very closely over the coming days. Perhaps it is just a blip in the models and subsequent runs will drop the storm/hurricane completely and we can all breathe a sigh of relief. I will post a detailed video discussion concerning this potential development later this afternoon once the morning model runs complete and are available.

M. Sudduth 7:45 AM ET July 7

 

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Window of development opportunity coming up?

It’s still early June and typically this time of the hurricane season means that things are usually quiet. Every once in a while we will get a June tropical storm or hurricane, but it’s not the norm. As most of you know, the season really begins to ramp up from about mid-August on. Usually….

This season might not be usual.

I am seeing the beginnings of signs that may point to a development window opening over the next week to ten days and beyond.

GFS and its ensemble members indicating a more favorable MJO state coming up for portions of the Western Hemisphere over the next couple of weeks

GFS and its ensemble members indicating a more favorable MJO state coming up for portions of the Western Hemisphere over the next couple of weeks

For starters, the Madden-Julian Oscillation or MJO is forecast by the GFS and Euro models to be moving in to the phase that often supports development somewhere within the Atlantic Basin. The MJO phenomenon is easy to think of as a period of fertility in the tropics, when deep convection can form and blossom, not just fizzle out and dissipate. While the MJO helps to enhance development it does not necessarily mean that development is a certainty.

The upcoming signal from the MJO is not especially strong but it is there (forecast to be there anyway) and could lead to better upper level winds over parts of the southeast Pacific and extending in to the western Caribbean and western Gulf. With water temps plenty warm in the region, all we need is a kick and it could lead to development in one basin or the other, maybe both. We will have to just wait and see.

If we look at the GFS operational model at the 850 millibar level which is about 5k feet up, we can see one week out from today that a wind shift or monsoonal trough begins to set up from the southeast Pacific, across Central America and in to the western Caribbean. This would act like a focusing mechanism for the air to come together or converge, probably leading to enhanced convection (thunderstorms) across the region.

GFS model at 168 hrs showing (yellow area) a wind shift and overall troff of low pressure stretched out over a large area, we call this a "monsson trough" and it can lead to development if conditions allow

GFS model at 168 hrs showing (yellow area) a wind shift and overall troughof low pressure stretched out over a large area, we call this a “monsoon trough” and it can lead to development if conditions allow

This large counter-clockwise “gyre” is so spread out that in and of itself it wouldn’t develop. We would need to see if an area of concentrated energy or vorticity breaks off and tries to develop out of this larger area of energy. If so, then a low pressure area could get going either in the Pacific or the western Caribbean – leading to the chance of a tropical depression or storm at some point.

As you can tell, the process is long and complex. I am not going to dwell on it day after day for two weeks but it is something to keep an eye on. At the very least, more rainfall than normal may be setting up for portions of Central America and it may lead to a named storm on one side of Central America or the other. Time will tell.

Then there is this interesting set up taking shape: The ECMWF (Euro) is indicating the possibility of an easterly wave (tropical wave) trying to develop way out in the deep tropics between Africa and the Lesser Antilles. Remember, water temps out this way are running above the long term average. If we do in fact see a strong area of energy emerge from Africa, it could take advantage of the warmer water and more favorable conditions overall  and try to develop some. This would be highly unusual and a significant sign in my opinion that this season could be quite busy. Again, time will tell.

We live in an age when computer guidance and satellite information allows us to see in to the future of weather forecasting better than ever before. These early warning signs are helpful since we should no longer be totally caught off guard. It may not prevent a “Labor Day hurricane of 1935” scenario in which case we saw a TS become a Cat-5 hurricane in a very short amount of time but the advances in technology now allows us to be more aware than ever that a threat from the tropics is looming (or could be looming). My point is, do not be alarmed or worried. There’s no reason for that. Instead, be aware. We were told the season could be busier than average and these are possible signs of that happening. So just take note and pay attention a little more than normal perhaps. Applaud the fact that we have such tools at our disposal and as long as we know how to interpret them, it can be a good thing. After all, with such much at stake along our coastlines (all of us, not just the USA), the more lead-time the better; at least I think so anyway.

I’ll have more on Monday during my video discussion.

M. Sudduth 1:20 pm ET June 9

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