Hurricane Season 2007

[Mat 'Sonic' Clark]

It’s been a weird old summer so far with the active jet stream we had for most of the winter not really packing up for the summer (it had a bit of a break during April) and its continued to hit us with a steady precession of lows. Unfortunately the jet stream has mostly been aligned with a dip over the eastern US seaboard and another dip over the UK.

This could be described as a bloody nuisance as its meant that lows have raced across the Atlantic and then stopped right on top of the UK bringing bad weather, blown-out surf and general depression all round.

So lets have a look at predictions for the hurricane season 2007:

NOAA (Posted 22 May 2007)
13 to 17 - Named storms

Dr. Gray's Tropical Storm Forecast (Posted 31 May 2007. Next update 1 Aug)
17 – Named storms

UKMET / ECMWF (Posted 19 June 2007)
7 to 13 – Named storms

So not much consensus there then. Anyone know of any other prediction out there? Mystic Meg perhaps?

Dr Gray’s ‘the daddy’ of hurricane season predication so his 1 Aug update may well be illuminating. Incidentally there’s quite an amusing and informative recorded presentation of Dr Gray’s here about TS activity and global warming.

http://ams.confex.com/ams/27Hurricanes/ ... 107533.htm

Here are some of the factors that effect tropical storm activity and have thus far kept the tropical Atlantic quiet:

Sea Surface Temperatures (SSTs)
The warmer the ocean gets the higher the probability is of Tropical Storms (TS) forming and the greater maximum theoretical intensity they can reach.

Current SST anomaly charts show slightly above average temps over most of the western tropical Atlantic whereas in the east near the Cape Verde islands is looking a little cool. Overall sea temps will continue to increase for a fair while yet.

https://www.fnmoc.navy.mil/products/NCO ... nomaly.gif

A worrying feature is that the Caribbean and Gulf of Mexico (GOM) have high anomaly’s and can support very intense hurricanes.(see http://wxmaps.org/pix/hurpot.html). Overall I get the feeling that should these SST trends persist we might see some real nasty hurricanes in the Caribbean and GOM that do a lot of damage but not quite the intensity of Fish (a Fish is a Hurricane that does not make landfall) we might hope for heading our way.

Wind Shear
Wind shear is a measure of the difference between winds at various levels of the atmosphere. TS need low wind shear to grow as high wind shear tears them apart. July has seen quite a lot of wind shear in the tropical Atlantic but August often sees this shear relax. You can see some lovely colourful wind shear charts here:

http://www.wunderground.com/modelmaps/m ... &domain=TA

You will need to add the wind shear chart in using the menu. I been looking at this over the past few days and it does seem that there is more of the red (less than 8 m/s) shear predicated as we head into August.

Saharan Air Layer (SAL)
Dust blowing about in the atmosphere coming from the Sahara can inhibit TS formation and growth. There’s been a lot of it about recently which is another reason for the quiet season so far.

http://cimss.ssec.wisc.edu/tropic/real- ... java5.html

Not found any way of predicting the SAL activity so it’s a real wildcard factor that could really reduce the number of TS’s we see.

El Niño Southern Oscillation (ENSO)
From what I can tell the main thing here is that El Nino suppresses TS formation because it increases wind shear over the tropical Atlantic. Neural or La Nina conditions cause less shear and are thus more conducive to TS formation/growth.

The current situation is that we have roughly neutral conditions. Things may go a little La Nina later on in the season.

These are the main factors I know about. There are others such MJO and sea level pressure but it’s all a bit chicken and egg and I don’t really understand it.

I will probably update this thread if I spot any interesting developments.

[stephh]

Cool, thanks for that very interesting reading. Being married to a weather forecaster and being an ex-meto myself I retain an interest in this kind of stuff, as well as its affects on the surf of course

[The Decorator]

That's brilliant Sonic. Nice and simple. I think most surfers attempt to understand whats going on in the Met world but get baffled by the physics.
Thankyou for putting it in English.

[Ferral]

Cool stuff, cheers!!

[Mat 'Sonic' Clark]

Thanks guys. Good to know you found it interesting.

Ben
Go ahead and do with it as you will. Cut out any bits you want if you think it needs to be more concise. There’s probably some spelling mistakes in there somewhere. I’ve just edited out a couple so hopefully not too many.

[Mat 'Sonic' Clark]

A quick update on the how the tropics are looking at the moment.

Although not even a tropical depression has formed yet since early June it does seem that the chances of a tropical system developing are rising quite a bit.

Some strong looking tropical waves are leaving the coast of Africa and are heading west.

http://www.ssd.noaa.gov/met8/eatl/loop-avn.html

These tropical waves are big areas of cloud and are one of the main sources from which tropical systems are born.

As they move across the Atlantic many of the global models have been flirting with the idea that they may spark of a tropical depression. These predictions by the global models are probably best described as an educated guesses and they often come to nothing. However the fact that many different models and various runs of those models keep showing some development means that there is at least a raised possibility of something forming.

Also of note is an area of disturbed weather near the Bahamas that the NHC is warning could develop.

http://www.nhc.noaa.gov/gtwo_atl.shtml

If you have been looking at the resent MagicSeaweed wind predictions you should have seen a very intense low forming to the west of Ireland around Thur/Fri the 2nd/3rd August. Normally I would blame such a strong low at this time of the year on spurious tropical development predictions by the global models (GFS in this case which Magicseaweed charts are based on).

However here it seems the GFS develops the low without much in the way of tropical development assumed on the part of the lump of cloud near the Bahamas. The lump does get pulled into the low but most of the strengthening seems to be down to power from the jet stream.

So the question arises what happens if the lump near the Bahamas does develop into a tropical storm of some kind. Well it could turn out something like the Canadian model (CMC) is forecasting. A very deep Low for any time of the year.

http://moe.met.fsu.edu/cgi-bin/cmctc2.c ... =Animation

Be warned however that the CMC is known for flights of fancy where tropical systems are concerned.

Whether or not a tropical system forms a look at the various models (GFS, UKMET ECMWF, CMC, NGP, GFS Ensemble) suggests a good swell producing low should form and give anything between a moderate to epic swell arriving around Sunday 5th August. Hopefully local winds won’t mess things up but it’s too far out, at the moment, to tell.

[Poo Stance]

Hey, just wanted to say thanks for posting your rantings on here about the weather. Any info which can help me get a surf is much appreciated. I love looking at the weather charts and trying to figure out if and when there will be waves. Its all part of the game if you ask me.

I mainly use Magic and windguru combined with the long and short range SLP charts and buoy readings. However, there seem to me so many factors to consider when it comes to long range forecasts, as I am slowly learning and trying to remember.

What I am curious about is which sites use which forecast models. You mention Magic uses GFS? Do you know if windguru does as well? Or which sites use which models.

Although I dont surf the East Coast much I do keep an eye on it during desperate times. A week or so ago there was a deepish low above Scandinavia and it seemed to produce a decent long range groundswell which Magic did not forecast. Is this because the forecast models dont enter data for that region above Norway etc. and thus miss potential swells created further north?

Or am I being a muppet?

Mucho gracias.

[stephh]

You might want to consider the location of the low pressure and the direction in which winds move around it and also the north sea has quite a low fetch so it takes quite a bit to create a large swell i.e think about the size of the Atlanic in comparison so although the conditions seemed right the geogrpahy and bathymetry may have been against it.

[Mat 'Sonic' Clark]

As stephh said the wind must be pointing in your direction and do this for a reasonable amount of time over the area where the swell is being generated. Fast moving lows often don’t produce as much swell as you think they will unless they are moving towards your location. Lows sometimes move across the top of the North sea quite quickly thus not producing much swell.

If you want to check what you see on magicseaweed against another WAM (wave amplitude model) go here:

https://www.fnmoc.navy.mil/CGI/ww3_all. ... swl_wav_ht

This WAM is based on the US Navy’s Forecast model known as the NGP. The NGP is not a great model but its okay in the short term (say up to 3 days ahead). The chart you see above is the swell wave height and shows only ground swell wave size as opposed to the GFS based WAM charts which are significant wave height. Significant wave height contains wave height due to low period swell (less than about 6 seconds wave period) and the longer period ground swell. The low period waves are generally due to fresh or stronger winds blowing on top of the swell and not only don’t add much size to waves at the beach but actually can reduce the size you get to surf although they make the swell look bigger on the WAM.

For longer range forecasting I would recommend looking at the GFS, ECMWF and GFS Ensemble. These 3 have been in good agreement about the Chantal low since about Saturday so I have felt pretty safe in predicting a decent swell from her based on their agreement.

[Poo Stance]

Thanks again for the info, I think I'm gonna bookmark this thread. Its like being back at school.

I will defo look into those forecast models. As well as the NGP one.

I dunno if I made myself clear in my 1st post (a common occurence). But what actually seemed to happen on the NE the day in question was that a swell was produced that Magic did not forecast. Well, they forecast it on the 1st day but nothing on day 2. But day 2 was better surf than the 1st (as in days the swell was hitting the beached).

So to reitterate my question. Can a weather system form north of Scandinavia and not picked up by the GFS model due to the fact that the system was positioned off the area which data is taken from to form the forecast models...ie. off the map?

Does this make sense? Sorry if I am being ignorant and wasting your time. Please say so if so.

[danny1]

MSW and the other buoy sites picks up the dominant swell. check spectrals for underlying swell...or just read the charts like the old days. keep things simple and score waves alone.

[mal-nourished]

thats why the sneaky little sth.coasts swells go undetected sometimes ...