Tropical Storm Dorian -- The first Cape Verde Storm

Tropical Depression 4 - later Dorian

Over the next 8-10 weeks disturbances from West Africa will increase in intensity as they emerge from the coast every 3-5 days.  By the middle of August, it is possible that every 1 out of 3  disturbances will develop into a tropical depression, storm or hurricane as it moves across the Atlantic.  Some fraction of these will become major hurricanes.  Throughout the summer thus far the steering currents for tropical cyclones have been been oriented to carry storms from east to west.  Whether this pattern will continue is uncertain, but if it significant fraction of these tropical cyclones may threaten the Caribbean, Central America, Gulf of Mexico, Eastern US seaboard and Bermuda.
Some of these disturbances will cause flash flooding and wind damage before leaving the African continent threatening life and property.

When I look at all of the data, it is still difficult to know if the genesis of Dorian is a sign of things to come.  The dust coming from the Sahara has been plentiful making the overall environment unfavorable for tropical disturbances to develop into tropical cyclones.  The next 10 days or so will tell much about the month of August.

Cape Verde storms as they are often called form in August because the waters have warmed, the African Easterly Waves are more intense and dust retreats to the north.   When this happens, they can pose a threat to the people of the Cape Verde Islands-- especially the capital (Praia).

Tropical Cyclone Dorian is expected to continue west over the next 5 days.

5 day track of Tropical Storm Dorian

But as you can tell, unless it is picked up by a trough, it will continue to move west with an aim on the Bahamas, the keys and Florida.  The GFS forecast has it turning north and possibly threatening the East Coast but it is much too early to tell and the skill of the models are not great for tropical systems 144 hours out. 

The early projections were 13-20 storms.  The next few weeks will tell if that is an accurate call, but I expect the waves to amplify as they move across West Africa.  The waters will be warmer and but the flow over the western atlantic will become more complicated, with vertical shear and mid-latitude troughs having a greater influence on the strength and direction of westward moving tropical disturbances.   
But for reference, in
2005 there were 27 named storms - by July 25th there were 6 named storms - today we are at 4
2008 there were 17 named storms - by July 25th there were 4 named storms- today we are at 4
2010 there were 19 named storms - by July 25th there were 2 named storms- today we are at 4
2011 there were 18 named storms - by July 25th, there were 3 named storms- today we are at 4
2012 there were 19 named storms - by July 25th there were 4 named storms- today we are at 4


So if there is going to be a busy season, we are on par with other busy seasons and should not let our guards down.  Remember.. Hurricanes are the deadliest and most destructive forms of storms because of their scale, power, various forms of destruction (wind, flooding, storm surge) and duration. 

Stay tuned,  the Cape Verde season has kicked off.

A weakened Chantal may be real trouble for Haiti today

This morning I woke up 3 AM for a bathroom break and happened to look at the structure of TS Chantal.  It had fallen apart.  I was not surprised because over the last few year, Tropical cyclone intensity in the Caribbean sea have been very difficult to forecast.  Since then, the thunderstorms have returned but the question remain is there a center of circulation or is it an open wave?

Visible image of Tropical Storm Chantal at 9:15 EST July 10

I believe that the circulation is still intact, but if you look closely at the track, it crosses just south of Haiti and with this Chantal, the heaviest rains and winds have been to the north of the center.  What this means is that Haiti should feel the full force of whatever Chantal has to offer, even in a weakened state.  Not obvious to the human eye, is that the mountains of Haiti force more thunderstorms because the air must rise and in the process cool and condense leading to more rain.  When the rain does fall, it comes down on a land surface that is 98% deforested according to some studies leading to strong runoff and flooding posing a threat to those in the way of rushing water and swollen rivers.

Also not obvious to the human eye from satellite is the aftermath of the Earthquake in 2010 and the displacement of so many people.  Because the tent cities or the establishment of stable homes for many Haitians remains out of the news we are unaware of what the people may face over the next 24 hours.  What is clear is that as of last October, when the rains of Hurricane Sandy impacted Haiti 54 people died as a result of the flooding.  The problem remains the same: unsafe conditions for the most vulnerable.  So while Chantal will not be a news maker because it is not a major hurricane and for that matter maybe only a weak tropical storm its impacts are likely to pose a serious challenge and threat to Haiti before it moves away later tonight.

A predicted busy hurricane season getting off to a fast start.

Tropical Storm Chantal just to the East of the Leeward Islands , Monday July 8, 2013

The 3rd named storm of the year, Chantal, is moving towards Barbados and the other Leeward Islands this evening.  Over the next 5 days it is expected to impact the Dominican Republic, potentially Haiti, Cuba, the Bahamas, Keys and possibly the SE US.  The environment is not great for this storm and it is likely to be impacted by mountains the vertical wind shear, which should keep it as a minimal hurricane.

National Hurricane 5 Day track Tropical Cyclone Chantal

Does this mean that we should not be worried about this storm??  Absolutely not.  Flooding with tropical disturbances continues to be a serious threat especially to Haiti which is expected to be near the path of Chantal.   For example, nearly 3000 persons died with Tropical Storm Jeanne went over northern parts of Haiti in 2004 before going on to be a hurricane. 

The science behind hurricane intensity has many uncertainties, and the models that are used to predict future strength can vary.  For example, over the next 5 days the Canadian model shows Chantal moving near Haiti, across Cuba and into Florida.  The ECMWF model, which correctly predicted Super Storm Sandy has Chantal fading out quickly, and the Hurricane WRF model shows the storm being weakened when passing over Haiti, only to gather strength off the coast of Florida.  The models are not perfect which means that you must still prepare if you live in coastal regions.  

What concerns me about the upcoming season, is that the weather disturbances in West Africa have picked up in the last week.  We normally see this happen in early August.   Forecast models are suggesting that the next two tropical disturbance may further develop later this week and early next week. Saharan dust, which tends to inhibit storms because of the dry, stable air does not seem effective at present.  Over the next month, the dust amounts will decrease and move further north.  At present steering currents for tropical cyclones are mainly west which would not favor storms turning north over the Atlantic but rather heading towards the Caribbean and Eastern US seaboard.  Sea surface temperatures are continuing to warm as the summer progresses and El Nino (which inhibits hurricanes through increased wind shear) is not present.  

 NOAA has projected 13 to 20 named storms this season.  Based on the current pattern this seems on target.  This may be bordering on conservative given that we have had 19, 18 and 19 named storms during 2010, 2011 and 2012.  The upswing in tropical cyclones over the last 18 years continues.  Its not too early to be prepared.  Stay tuned.. we are just beginning.