Bertha strengthened
considerably overnight and into this morning and went from a moderate
tropical storm yesterdy afternoon to a borderlin cat 1/2 hurricane as
of 11am today, with winds of 90 mph. An impressive feat for early July
no doubt. In fact the satellite apperance of Bertha has continued to
get better today and and she may already be a category 2 storm as of
now and could end up a category 3 storm! Bertha is moving between west
and west northwest currently with move of a NW jog the last few hours.
Below is the latest impressive IR satellite image with hurricane model
tracks superimposed and also the latest visible image.
The synoptic reasoning and thinking for the track of Bertha is unchanged from yesterday. If there has been a trend it has been further east with the turn to the NW and north in the day 3-5 range with most models now turning Bertha east of Bermuda. However there is still the caveat of whether or not Bertha will be completely re-curved by this trough or hang around and wait for a new set of steering currents to develop. This is why we can not toally close the book on Bertha quite yet. Most global model guidance depicts another trough moving into the NE this weekend, and exerting yet another poleward tug on Bertha, but it is possible this trough doesnt get the job done either. If it doesnt Bertha could stall again and wait for yet another trough or for a western Atlantic ridge to build in and push Bertha back westward. As of now, no model guidance shows Bertha impacting the US. However the threat is certainly not over yet untill we get closer to the medium range period day 5-9 and the eventual pattern becomes clear. The threat is esepcailly not over yet for Bermuda or the Canadian Maritimes.
I do think that Bertha may reach category 3 status sometime the next 24-36 hours before a less favorable environment shapes up with some modest increase in shear.
The synoptic reasoning and thinking for the track of Bertha is unchanged from yesterday. If there has been a trend it has been further east with the turn to the NW and north in the day 3-5 range with most models now turning Bertha east of Bermuda. However there is still the caveat of whether or not Bertha will be completely re-curved by this trough or hang around and wait for a new set of steering currents to develop. This is why we can not toally close the book on Bertha quite yet. Most global model guidance depicts another trough moving into the NE this weekend, and exerting yet another poleward tug on Bertha, but it is possible this trough doesnt get the job done either. If it doesnt Bertha could stall again and wait for yet another trough or for a western Atlantic ridge to build in and push Bertha back westward. As of now, no model guidance shows Bertha impacting the US. However the threat is certainly not over yet untill we get closer to the medium range period day 5-9 and the eventual pattern becomes clear. The threat is esepcailly not over yet for Bermuda or the Canadian Maritimes.
I do think that Bertha may reach category 3 status sometime the next 24-36 hours before a less favorable environment shapes up with some modest increase in shear.
"Bertha holding steady, still some uncertainty in future track." *7/6/08 2pm*
There has been little change in the strength of Bertha since yesterday, there has been some convective pulsing and this morning has featured a pretty good pulse, but for the most part there has been no real net weakening or strengthening. Below is the latest IR image with the 12z early dynamical/consensus model
The basic forecast scenario is unchanged from yesterday, since this time yesterday the models have come more in line with the storm turning NW begnning around 56-60W with a NW movement with the storm getting between 65-70W as it's western-most point, most more towards the 65W longitude line. This occurs because the models are predicting an upper level trough to move into the Great Lakes and northeast US by the middle to later part of this coming week, which will in turn induce a more northerly motion. I have included the 500mb and seal level pressure forecast valid for 0z Thursday from today's 12z GFS, notice the location of Bertha, a weak (likely too weak by this model) 1015mb low around 65W north of Puerto Rico and also the 500mb trough in the Lakes region (Depcited by the solid black line) and also a cold front moving thru the eastern US wednesday evening. This trough will help to induce the NW turn later this week.
So then the main question becomes is this trough strong and deep enough to totally recurve Bertha or just turn it NW for a while before leaving it behind? The latest 12z GFS model shows that the storm is left behind as this trough departs into the North Atlantic this weekend. Bertha stalls around 27N,68W before another trough comes into the northeast early next week and turns Bertha north into Canadian martimes. This same type of scenario is shown in the 00z ECMWF, as does the 0z Canadian model. This scenario would mean no threat to the US but a threat to Bermuda and the Canadian maritimes. Right now I like the stall idea by this weekend, and odds would favor another trough moving into the east next week to recurve this off the east coast.
But here are the caveats. One while confidence is somewhat high in this first trough tugging Bertha northwest in the day 3-5 time frame, confidence is not as high in the followup trough in the day 7-9 range. There are the usual caveats of this being relatively far out in time for a model to accurately predict, but also even if the trough is real it could evolve differently than what the models show. For instance the models are insisting a piece of this trough breaks off over the southeast US and off the south Atlantic coast and becomes a cut off low. This could mean a different scenario if per se Bertha is a little further south than what the models show at this time or this trough splits occurs and the northern end of the trough isnt very strong or deep. This could mean another stall and a possilbe turn more westerly as a ridge builds in to the north and the cut off low in the southeast could steer the storm west or northwesterly. It is just too early to say. Odds right now are still very much in favor of a recurve both from climo but also from how the pattern has been the past 3-4 weeks with frequent troughs in the Lakes and northeast. But there are still enough questions to still be wary.
As far as intensity goes, Bertha will probably slowly strengthen as show by the hurricane intensity models below into a strong tropical storm and perhaps a weak hurricane by Tuesday or Wednesday. However, it seems likely at least some shear will impact Bertha by mid week as the first trough bypasses her to the north, thus any strengthing would cease or some weakening could occur. Beyond this more strenghening could commence before it interacts with the 2nd trough early the following week. I think Bertha will be in the 70-80mph range by Wednesday morning and probably hold in the strong tropical storm weak cat hurricane range thru the weekend. Stay tuned, we have all week to follow this storm.
"Tropical Storm Bertha Churning out in the Atlantic, threat to US low, but cant be ruled out yet." **7/5/08 3pm**
Well an early start to the
Atlantic Cape Verde season for sure this year. Could this be a
harbinger for things to come? Well yes and no I think. I do think we
are in store for an active season, with above normal Cape Verde, long
tracking storms, but I dont think we are going to see a historically
active season, more in the 13-15 named storm range. IT does tell me,
that obviously, we have to take any wave seriously that moves off of
Africa now and that any could develop for the rest of the season. In
other words, it is already time to be vigilant, a little earlier than
most years.
On to Bertha. Bertha is holding her own today as a weak to moderate tropical storm with winds of 50 mph at 11am. Bertha is already rather far north (above 15N before 40W) for a storm that far out to have a good shot at making it to the US. Now it isnt impossible, but obviously the further north the storm gets the better chance a passing trough to it's north will recurve it out to sea before a US landfall. Bertha is also fighting sea surface temperatures in the far east Atlantic that are warm enough to support a tropical system, but are not near their peak warmth (usually mid August to mid September). So this makes the forecast of any rapid strengthening the next few days dubious. Here is the latest IR satellite image with the 12z early dynamical and consensus models overlaid on it, which you can find here http://raleighwx.easternuswx.com/models/satellite/satatcf.html
Many of these models take Bertha to around 20-25N and 60-65W by Wednesday/Thursday time frame. A weak trough around 50W will bypass Bertha to the north on Monday/Tuesday which should not re-curve it but just create a more WNW track than W. Most of the intensity models http://raleighwx.easternuswx.com/models/atcf.html
show a steady intensification to the 55-65kt range over the next 3-5 days which would mean a strong tropical storm to potentially weak cat 1 hurricane. The GFDL and GFDT models, which are the same model except the GFDT uses the GFS tracker function, take the storm 85 kts in 5 days. I DO NOT expect any rapid intensification from Bertha and think a slow and steady strengthening into a strong tropical storm weak cat 1 storm in 4-6 days is certainly possible and a good forecast.
Beyond this, right now the key to where Bertha will go in the day 5-10 range will be the expected progression of troughs thru the great Lakes and northeast US. Below is the latest ATCF forecast tracks for 18z.
As you can see the models are now starting to show a turn to the NW by late in the period. The key will be will a trough be strong enough in the 6-8 day period to turn the storm, or will these trough(s) trend weaker. Remember a few days ago the models where showing a recurve between 50-55 W and as of now, it doesnt look like that trough will do the job. Predicting trough strength and placement 6-8 days out is tricky and will likely change. Right now the pattern favors frequent trough passages thru the midwest and northeast, so odds favor some sort of turn in the 5-10 day period but rather it is a total recurve or a turn and stall or not much of a turn is still up for debate. The latest ECMWF (12z Saturday) is showing a recurve around 70W but then phases this with a trough and turns it west towards the NE coast by day 10 (not likely). The 12z GFS is much weaker with a trough in the day 6-8 and a weak Bertha approaches the east coast before turning and staying off shore.
Right now, climo doesnt not favor a threat from this storm, nor does the current weather pattern. Odds favor a trough sometime in the next 5-10 days recurving Bertha off the US coast. Bermuda is another story and this is one they need to watch. I will try and update as I get time and especially if things change the next several days.
On to Bertha. Bertha is holding her own today as a weak to moderate tropical storm with winds of 50 mph at 11am. Bertha is already rather far north (above 15N before 40W) for a storm that far out to have a good shot at making it to the US. Now it isnt impossible, but obviously the further north the storm gets the better chance a passing trough to it's north will recurve it out to sea before a US landfall. Bertha is also fighting sea surface temperatures in the far east Atlantic that are warm enough to support a tropical system, but are not near their peak warmth (usually mid August to mid September). So this makes the forecast of any rapid strengthening the next few days dubious. Here is the latest IR satellite image with the 12z early dynamical and consensus models overlaid on it, which you can find here http://raleighwx.easternuswx.com/models/satellite/satatcf.html
Many of these models take Bertha to around 20-25N and 60-65W by Wednesday/Thursday time frame. A weak trough around 50W will bypass Bertha to the north on Monday/Tuesday which should not re-curve it but just create a more WNW track than W. Most of the intensity models http://raleighwx.easternuswx.com/models/atcf.html
show a steady intensification to the 55-65kt range over the next 3-5 days which would mean a strong tropical storm to potentially weak cat 1 hurricane. The GFDL and GFDT models, which are the same model except the GFDT uses the GFS tracker function, take the storm 85 kts in 5 days. I DO NOT expect any rapid intensification from Bertha and think a slow and steady strengthening into a strong tropical storm weak cat 1 storm in 4-6 days is certainly possible and a good forecast.
Beyond this, right now the key to where Bertha will go in the day 5-10 range will be the expected progression of troughs thru the great Lakes and northeast US. Below is the latest ATCF forecast tracks for 18z.
As you can see the models are now starting to show a turn to the NW by late in the period. The key will be will a trough be strong enough in the 6-8 day period to turn the storm, or will these trough(s) trend weaker. Remember a few days ago the models where showing a recurve between 50-55 W and as of now, it doesnt look like that trough will do the job. Predicting trough strength and placement 6-8 days out is tricky and will likely change. Right now the pattern favors frequent trough passages thru the midwest and northeast, so odds favor some sort of turn in the 5-10 day period but rather it is a total recurve or a turn and stall or not much of a turn is still up for debate. The latest ECMWF (12z Saturday) is showing a recurve around 70W but then phases this with a trough and turns it west towards the NE coast by day 10 (not likely). The 12z GFS is much weaker with a trough in the day 6-8 and a weak Bertha approaches the east coast before turning and staying off shore.
Right now, climo doesnt not favor a threat from this storm, nor does the current weather pattern. Odds favor a trough sometime in the next 5-10 days recurving Bertha off the US coast. Bermuda is another story and this is one they need to watch. I will try and update as I get time and especially if things change the next several days.