Science Tropical Weather

Atlantic Hurricane Season 2013. An Active Season??

The 2013 Hurricane season which began June 1st and both the NOAA and ENSO reports are out and the 2013 hurricane season will most likely be a much more active season than the previous years. This hurricane season may be a dangerous one for many in the East Coast of the US, especially the Florida East coast, Florida Keys and the Gulf coast of Florida and possibly even the Caribbean but we will get to that a bit later.

So lets start with the basics of why this season is expected to be different. Beginning with ENSO or El Niño Southern Oscillation. ENSO is a climate pattern in the equatorial Pacific. Many might wonder what does the equatorial Pacific have to do with storms in the Atlantic. Globally, what happens in the Pacific can induce what happens in the Atlantic. Now with ENSO, there are basically three phases. One is a cool stage, another is a warm stage and there is also a neutral stage.

To have a cool stage, abnormal SST’s (Sea Surface Temperature) must have five consecutive overlapping 3-month periods: for example – (June, July, August), (July, August, September), (August, September, October) or more and the abnormal SST’s must be -0.5 degrees Celsius or lower. This also known as an La NiñainfoLa NiñaLa Niña is associated with cooler than normal water temperatures in the Equatorial Pacific Ocean. During an La Nina, abnormal SST’s can allow anticyclones to develop due to convergence (upward motion) which can help induce the possibility of development of a tropical cyclone.

Conversely, a warm stage must have the same five consecutive overlapping 3-month periods: or more and the abnormal SST’s must be at .05 degrees Celsius or higher. This is known as an El NiñoinfoEl NiñoEl Niño is associated with warmer than normal water temperatures. During an El Niño, storms in the Pacific will have an impact in the Atlantic. The possibility of tropical cyclones in the Atlantic developing is reduced, usually due to vertical shear. The Neutral stage is stage between the two and normally will only last a short period of time. The Neutral stage basically has no impact on the Global Weather patterns.

Next up, the Atlantic Tripole. When there is an Atlantic Tripole, basically what is happening is that in the tropical area of the Atlantic Ocean you are have warm waters to the south, and then from the tropical area to approximately 40° north latitude you now have a large of much cooler waters. From 40° north latitude northward, there would be an area of warms waters again. Since this is not the normal pattern, sometimes this can have an increase in the amount of convection and lift somewhere between Africa and the Leeward and Windward Islands. This can help the development of any tropical systems.

Hopefully, you are still with me as we talk about the NAO (North Atlantic Oscillation) and the the warm SST’s in the tropical area and the MDR (Main Development Region), MJO (Madden Julian Oscillation), and finally the PDO (Pacific Decadal Oscillation). Please note: I have purposely have left out the IODinfoIndian Ocean DipoleA coupled ocean and atmosphere phenomenon in the equatorial Indian Ocean that affects the climate. in this discussion. Although it can a contributing factor, I felt we have enough information as is and did not want to add any further possible confusion.

The NAOinfoNAONorth Atlantic Oscillation describes the strength of the surface pressure difference that is between the Azores High and the Icelandic Low. The NAO has two phases: a Positive phase and a Negative Phase. With a Positive NAO you have a stronger than average high across the Atlantic, this will increase the trade winds to the south of it. Those trade winds run across the eastern portions of the Atlantic and into the Caribbean. The stronger trade winds allow for increased evaporation cooling which then allows for cooler than average SST’s. Conversely, with a Negative NAO, the Azores High and the Icelandic Low are now weaker than average. So now with a weak high the trade winds will be much calmer allowing the SST’s to increase considerably. The NAO while it is a big player with the SST’s, the NAO also is a player in tropical cyclone development. Consider this, with quicker than average trade winds, any tropical waves will have very rapid movement as they come of the coast of Africa. The tropical waves will find it difficult to consolidate or strengthen if the forward motion is over 20 MPH or more. Not only can the tropical wave find it difficult to strengthen but this can lead to speed shearinfoSpeed ShearSpeed shear is the change in wind speed with height..

The NAO is also a player in the track of tropical cyclone. Recalling that during a Negative NAO, the Azores high is typically weaker but it is oriented west to east and closer to the US Southeast coastline. During a Negative NAO, any troughs on the East coast will typically be weaker and recurving of a tropical cyclone will be much more difficult to do. A Positive NAO on the other hand will allow recurvature much easier. Please note that the short term timing essentially will govern the track of a tropical cyclone, not the long term mean.

The abnormally above average SST’sinfoSST'sSea Surface Temperature  is another concern this year especially in the MDRinfoMDRMain Development Region. The MDR is a very large area, extending from the Caribbean Sea to almost the coast of Africa. A warmer than normal MDR will provide the feeding fuel for the beginning of the development but also help nourish tropical cyclones. The minimum water temperature needed for a tropical cyclone to begin development is approximately 26°C or (79° F) and a depth of at least 160 feet but there also other factors needed.

Now let’s get to the MJOinfoMJOMadden Julian Oscillation. What is the MJO?  The MJO is an eastward progression of large regions of both enhanced(positive) and suppressed(negative) tropical rainfall. Simply put, there are two completely different phases with the MJO. One is a negative phase and the other is a positive phase. The MJO is different than ENSO as the MJO moves eastward at between speeds but anywhere from 8- 18 MPH across the different regions in the tropics, crossing the Earth in 30 to 60 days (with an average of 40 days). As it heads eastward and eventually into the East Pacific and then into the Atlantic the two phases are completely opposite of each other. In a Negative phase, lift is subdued and development of a cyclone is harder, but not impossible to have. In a Positive phase, now moisture and lift (upward motion) into the atmosphere allows easier development of a tropical cyclone (increased convection/thunderstorms activity).

Lastly, the PDOinfoPDOPacific Decadal Oscillation. The PDO is a pattern of change in the Pacific Ocean’s climate. The PDO is easily recognized with cool or warm surface waters in the Pacific Ocean (north of 20° N. latitude). During a Negative or cool phase, the west Pacific  becomes warm and the eastern ocean is cool. Conversely, during a Positive or warm phase, the west Pacific becomes cool and the eastern ocean is now warm. So again you are wondering how does that affect you if you live on the US east coast? During a Negative phase and in the Atlantic basin, the rising of air helps upward lift and possibly allowing more convection which can help promote tropical cyclone development.

So now that you have had a short lesson in Meteorology 101, what does all this mean? In one sense, not a thing, but certain patterns may appear this season and may allow for possible stronger storms and also a much higher chance of landfall somewhere along the US Eastern coast. The past few years, many of the storms were recurved and they went out to sea. TroughsinfoTroughAn elongated region of relatively low atmospheric pressure, often associated with fronts would develop, head east and pull the storms up and keep the storms away. This year appears to be different. A more pronounced and elongated Bermuda high will remain allowing any tropical cyclones to be caught under the ridgeinfoRidgeA ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough. If the Bermuda high weakened enough, and a storm was under the ridge of the high and near the southwestern (or the periphery) of the ridge. This may allow the storm may follow around the edge of the high. This may allow a more northwestern track instead of a western track and possibly towards the East Coast of the US. Any storms much further west and if the ridge is still strong would possibly be in the Caribbean and if a system in the Caribbean and if there were a trough over the Plains of the US, this may have a storm heading toward the US Gulf Coast.

Using those different meteorological basics we talked about earlier, lets see why the possible reason why this may be a more active hurricane season.


The ENSO is now in a neutral stage. Looking at the SST anomaly chart you must recall that for either an La Niña or El Niño ±o (either -.05° Celsius or .05° Celsius) for the last 3 months or more. Notice that is the chart both NINO 4 and NINO 3.4 have not reached the threshold needed. The short term forecast is that we will be in a neutral stage with a cold bias. Long term forecast is a bit cloudy but it is forecast that later in the season we may have a weak La Niña.

sst anomaly

Atlantic Tripole

Now it is time again for the Atlantic Tripole. Although the chart below is not a true representative of an Atlantic Tripole, it does show the different areas. The black arrow designates the warm waters and the red arrow designates the cooler waters. In a non-Atlantic Tripole, the areas north of 40° are much cooler waters. A bit later in the season the southern Atlantic (the tropical area) is expected to be much warmer. With much warmer waters and tropical waves emerging from the coast of Africa those tropical waves have a better chance of possibly developing into something tropical.

sst anomaly tripole



Our attention is now focused in the NAO. All indicators reflect a Positive NAO. The Azores high is further south which can allow tropical systems to head further West or WNW. In the chart below is the latest NAO forecast both the Observed and Ensemble. The black line being the observed and the smaller lines from the different ensemble members. It you note that nearly all are indicating a Positive NAO. If you may recall from your Meteorology 101 course, a Positive NAO allows the latitudinal displacement of the Azores high further southward. For the time being the NAO is in a Positive phase but it is expected later in the season for the NAO to go into a Negative phase.

nao chart


SST’s In The MDR
The abnormal high SST’s in the MDR is something I cannot emphasize enough. Recalling that a tropical system’s primary energy source is the evaporation of water from the ocean surfaceinfoInfo Also known as latent heat, higher SST’s may allow easier development of of tropical wave, although there are other factors needed.

sst analysis
SST Analysis



As discussed earlier, the MJO progresses eastward with two different phases. At this time, the MJO is entering the East Pacific and Western Caribbean is a Positive phase. In the Positive phase, upward motion or lift and moisture allows easier development of convection/thunderstorms. The chart below can be a bit confusing but itself is a simple one once you comprehend how it works.

mjo full

Looking at chart, you will notice that there 8 Octants with Octant 1 at the lower right and Octant 8 at the upper left. You will also notice near Octant 6 a legend for some of the different weather models with different a color for each. Next, you will notice a circle in the middle. You will also see (sometime difficult to read) numbers which correspond the different days (or index). For simplification, if the index is within the circle the MJO is considered weak. If the Index is outside the circle, then the MJO is considered a strong pulse. The MJO in the diagram moves counter-clockwise direction even though the MJO itself runs from west to east. You might have noticed the RMM1 and RMM2. Although this is something we need to worry about but the RMM1 and the RMM2 are simply mathematical methods which combine cloud amount along with winds at the upper and lower atmosphere. This provides a measure of the strength and location of the MJO.
To make things easier, we are only going to need octants 8 (East Pacific & Gulf of Mexico/Caribbean) and octant 1 which is the Atlantic basin. In the example above, near 28 in octant 1, you can see that several models (UKMET, GEFS, ECMF, CANM) all are outside the circle. Please note though, even if the MJO diagram is showing the different strong pulses within the different models, this does not always mean a development is imminent. This just means that there is usually upward motion or lift in the region and the possibility of easier thunderstorm activity.


Although not stated earlier, the  PDO is a long-term ocean fluctuation of the Pacific Ocean and wanes and waxes approximately every 20 to 30 years. When there are changes in the locations in the Pacific between the cold and warm water masses, they alter the path of the jet streaminfoJet StreamFast flowing, narrow air currents found in the atmosphere.. The easiest way to state this is that the jet stream in the northern hemisphere delivers the the different storms across the US. In this case the PDO is in a Negative (or cool) phase and this will will try to steer the jet stream further north over the Western portion of the US but this also allows for possible tropical cyclogenesisinfoTropical CyclogenisisCyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area). in the Atlantic. The diagram below shows the different warm and cool phases.

pdo warm and cool phases



Although no one (not even the Specialists at the NHC) can tell exactly what the 2013 hurricane season will be like, using some the factors I outlined in this post, it does appear that this hurricane season will be a much more active season. When you have a Negative PDO, a Neutral ENSO but with a cold bias, a Negative NAO, extremely warm SST’s in the MDR, along with a Atlantic Tripole, all these factors (along with others we have not discussed) do seem to favor a season of much higher activity. It is unrealistic to even try as to where (if any) landfall will occur but just using the above factors along with some analogue years for comparison, areas of risk for possible cyclone landfall are higher in some locations whereas other will have a lower risk. The graphic below is a generalization and is not meant to alarm those in the higher risk areas.



Okay, now that wasn’t too bad was it. Hope you enjoyed your short class of Meteorology 101 and that it hopefully paid out and I hope you learned a little in the meantime. Please note this was a generalization of what the 2013 hurricane season might like and many contributing factors may and will usually change throughout the hurricane season. If you are not sure on any of the items discussed, please feel free to Contact Me at the top of the page. Remember, I am not a trainer meteorologist. As with any storm, please check with your local WFO or the NHC>

Lastly, and most importantly, please be sure to put together your Emergency and Hurricane Survival Kit if you have not already done so. If you have pets, please be sure to have plans to care for them. Check your homeowners or renters insurance before any possible storms develop and ensure you are properly covered for property damages and I would highly recommend that you also take flood insurance.



Tropical Weather

Tropical Storm Tomas Reborn

After losing tropical storm status early in the morning, Tomas has been able to regain it’s structure and reorganized during the day and as of the 5PM advisory from the NHS, Tomas has been upgraded to Tropical Storm status. Now with Tomas reorganizing and with light vertical shear and warm SST’s, intensification is forecast. SHIPS rapid intensification index is showing a 50% chance of 30 knot strengthening within the next 24 hours. An argument can be made that with the current organization of Thomas, that is a little too much. The new intensity forecast is a compromise between SHIPS and the LGEM model forecast. Although it is not out of the question but here is the possibility that Tomas may become a hurricane before land interaction stops any further intensification. After passing Hispaniola, southwesterly wind shear will cause Tomas to weaken.

IR Satellite image of Tropical Storm Tomas
Visible Satellite image of TS Tomas
AVN Satellite image of TS Tomas
Vapor Satellite image of US and TS Tomas
Models for TS Tomas
Tropical Weather

Hurricanes Igor, Julia, Karl & PreInvest PGI45L

Hurricane Igor still a threat to Bermuda with winds of 120MPH and is still a Category 3 storm. The inner eyewall of Igor has been broken on the west side, but there is still time for this to regenerate. Igor is an environment of very light shear and warm SST’s. Within 48 hours, Igor will start to feel the effects of cooler waters and some gradual increasing of south to southwesterly shear. The steering flow of a subtropical ridge will keep Igor on a NW – NNW for the next few days. After that forecast period, a series of strong short wave troughs that is located in the Northeastern US will turn Igor NE.

Visible Satellite image of Igor
Visible Satellite image of Igor, SW Troughs

Hurricane Julia is slowly decreasing in strength mostly due to an increasing N to NW shear from the large upper-level outflow from Hurricane Igor. The outflow is from top of the storm Igor and rotates clockwise. Continued weakening is forecast in two of the models and the Dynamical models are forecasting dissipation with Julia being absorbed within the circulation of Hurricane Igor.

Visible Satellite image of Hurricane Julia
Visible Satellite image of Igor & Julia with outflow

Dangerous Hurricane Karl is a Category 3 storm. The eye of Karl will be making landfall in Mexico within minutes, if not now. Karl will start to lose strength once the eye has made landfall due to the interaction with land and the high mountains in Mexico. Major flooding will be a problem.

Visible Satellite image of Karl
AVN Satellite image of Karl

ADDENDUM: The Eye of Hurricane Karl has made landfall just northwest of Veracruz, Mexico – just before 2PM EST.

Pre invest PGI45L is still a very series of thunderstorms associated with a broad low pressure system. Since this is the peak of the hurricane season and this area is in the Cape Verde Islands – this system has to be monitored. I feel any development, if any, will probably head NW and away from any land masses.

IR Satellite image of PGI45L
AVN Satellite image of PGI45L
Tropical Weather

Hurricane Julia, Hurricane Igor, Invest 92L (now TS Karl), PGI45L

Tropical Storm Julia had been upgraded to Hurricane Julia as of the 5:00am advisory. Julia is in an area with decent SST’s which will allow for some possible further intensification for at least another day or two. After that period, and even though Julia will still be in warm waters, Julia will be feeling the North to Northeasterly shear basically the outflow from Hurricane Igor. Julia is forecast to make a NW heading due to a mid to upper level trough for 24-48 hours, then a sub tropical ridge will cause Julia to return back on a WNW heading for a few days. Beyond that forecast, the models are in agreement on Julia turning NW then NNW as Julia will be along the Western periphery of at previously discussed ridge.

IR Satellite image of Hurricane Julia
Models for Hurricane Julia

Dangerous Hurricane Igor has finally started to turn toward WNW then will make a turn toward the NW. A weakness in the sub tropical ridge will make Igor turn to the NW and later a NNW. Exactly when these turns will happen in unclear. The U.S. coast should have no problems except possible swells, but Bermuda might be right in Igor’s way. If Igor delays these turns then Bermuda may get the N and NE(strongest) side of the storm. If Igor starts the turns much earlier then Bermuda make get the weaker side of the storm or just possible Tropical Storm force winds. As Igor continues to gain latitude, Igor will begin to be in cooler waters and lose some of his strength – possibly a Category two or high Category one.

Visible Satellite image of Hurricane Igor
AVN Satellite image of Hurricane Igor
Steering Layer Map
Models for Hurricane Igor

Invest 92L today seems the it is finally trying to get something together. Good convection has been present for several hours with the exception in the east and southeast quadrants. It does seem to have some very good, but not excellent cyclonic spin. If 92L can continue to do as well during the rest of the day, 92L may become a tropical depression. Tropical storm is not out of the question but I doubt it as 92L is running out of time before it comes ashore in the Yucatan.

As of the 5:00pm Advisory Invest 92L has been upgraded to Tropical Storm Karl. TS Karl has maximum winds of 40 MPH but is the forecast is expected for Karl to strengthen slightly. Due to land interaction, any increase in strength should be gradual.

Visible Satellite image of TS Karl
IR Satellite image of TS Kark
Models for Invest 92L

PGI45L is a system still over the African continent but will be coming off the coast soon. This a large system and will be monitored for further development.

Eumetsat Satellite image of PGI45L
Tropical Weather

Dangerous Hurricane Igor, & Tropical Storm Julia

Dangerous Hurricane Igor is now a Category 4 and there is a possibility it may attain Category 5 status. Igor will be going though a ERC, and during that time Igor will weaken slightly but will still be a major hurricane. Unfortunately, no one can tell when the ERC will start. Igor is still on a Westward track but within 24-48 hours, Igor should begin a WNW track due to a long wave trough in the Western Atlantic. There is some disagreement about the trough flattening out in about 3 days, which would bring Igor back on a westward track. This will have to be seen and the forecast discounts the possibility for the moment.

IR Satellite image of Igor
IR Satellite image of Igor
Water Vapor Satellite image of Igor
Steering Layer
Models for Igor

TD Twelve which is in the far Eastern Atlantic has been upgraded and is now Tropical Storm Julia as of the 11PM advisory. TS Julia is still having some moderate Easterly shear but this will be decreasing within 12-18 hours and is forecast to remain light for the next few days. TS Julia will be in very warm SST’s and this will allow steady strengthening so Julia is forecast to attain hurricane status. Thereafter, Julia will start to move into cooler SST’s and also will start in an area of increasing southwesterly shear. Julia will be on a WNW track and then later the storm is forecast to turn NW due to a weakness in a mid-level ridge.

IR Satellite image of TS Julia
Water Vapor image of TS Julia
Wind Shear of Eastern Atlantic
Models for TS Julia

A very large tropical disturbance still inside Africa will be rolling of the coast soon. This is another of the train of waves coming off Africa.

IR satellite image of next wave
AVN Satellite image of next wave
Tropical Weather

Invest 92L, TS Igor

A wave in the eastern Caribbean, just south-southeast of the Windward Islands has become better organized and has been designated as Invest 92L. Once Invest 92L can move away from the South American coast, 92L will be in a position to strengthen and develop into a tropical cyclone. Most models are in agreement of 92L developing into a hurricane and the flow will be a W to WNW movement. An outlier model (the Canadian CMC) model has it closer to Cuba and possibly Florida. Shear will be very light and the environment will be conducive for further development. The pattern for this system will be for 92L to have landfall toward the Yucatan and if it follows a more WNW-NW flow it will get into the southern GOM and this might be another threat to Texas if it holds together.

IR Satellite image if 92L
Visible Satellite image of Invest 92L
Wind Shear West Atlantic/Caribbean
Models for Invest 92L

Tropical Storm Igor overnight and this morning was being assaulted by moderate easterly shear but as the day progressed the shear began to relax a little and this allowed deep convection within the center to form along with an expanding convective field. There was a weak low to the northeast of Igor but that has been absorbed by Igor. The shear will be relaxing over the next few days along with warm SST’s and a very moist envelope, Igor will be in an environment conducive for steady intensification. Both Statistical and Dynamical models are in agreement for Igor to be a hurricane with 2-3 days. Further intensification is also forecast. There is a mid-level ridge to the north of Igor and this will keep Igor on a W to WNW track along with a gradual increase of forward speed. On day 4 Igor will be be in the Central Atlantic and will be near a trough which should cause Igor to turn toward the NW. Exactly how much of a turn and when has caused the different models to slightly disagree. Some models tend to believe that Igor will follow a path similar to Danielle and therefore the will not affect Bermuda where as other models are taking a slower track and taking a path similar to Earl being between the coast of the SE U.S. and Bermuda.

IR Satellite image of TS Igor
Visible Satellite image of TS Igor
Shear Map of the Eastern Atlantic
Models for TS Igor
Tropical Weather

Tropical Storm Hermine

What was Invest 90L then updated to TD Ten has now been upgraded to Tropical Storm Hermine. Overnight, TS Hermine started to head N which did give it a little more breathing space to develop. It is still forecast to make the turn toward the NW but when that turn will happen is still unclear. The track for Hermine has shifted right from the previous one and this places TS Hermine right again the Mexico/Texas border. TS Hermine has a very ragged CDO(Central Dense Overcast), but unless it start to make the turn to the NW, the CDO should begin to have a better overall appearance. Additional strengthening is forecast but I don’t think it will have enough time to become a minimal hurricane even though the SST’s are in the 30°C-31C° range. I do believe the forecast track will need to be adjusted slightly to the right again as the ridging over the northern Gulf has been slow in coming.

Visible Satellite image of TS Hermine
IR Satellite image of TS Hermine
Water Vapor Satellite imagery
Models for TS Hermine
Tropical Weather

Hurricane Earl, TS Fiona, and now TD Nine

Since this is the peak of the Hurricane season the tropics are hot and the trains of storm keep coming off the coast of Africa.
Hurricane Earl is now down to a Category 3 storm and the east coast from NC to Nova Scotia may get some effects from Earl. Earl is over very warm waters and also has a very good Cirrus outflow in a directions with the exception of the south, but Earl is now experiencing some SW vertical shear of 15-20 knots. There is also some mid to upper level dry air which is wrapping around portions of the storm. This should continue for 36 to 48 hours, but after that Earl will be over some cooler SST’s and this should begin to drop the intensity levels. The forecast is for Earl to be extratropical within 96 hours.

Satellite image of Earl
Models for Earl
Satellite image of Earl & Fiona
Wind Shear

Tropical Fiona has become better organized today. Fiona looks much better with the exception of mid level dry air in the northern quadrant. The forecast for Fiona also better than yesterday which has Fiona dissipating in 48 hours. Most of the latest guidance now believe that Fiona will be a hurricane short term – possibly as soon a late tomorrow even though Fiona is going though some moderate shear. Soon after, there will strong northeasterly shear, mostly due to strong upper level winds associated from Earl. The pattern in a few days has Fiona rapidly weakening.

Satellite image of Fiona
Models for Fiona


The tropical wave that came off Africa yesterday and was designated as Invest 98L this morning has now been classified as Tropical Depression Nine. A deep-layered subtropical ridge will keep TD Nine on W track for the next few days. By days 2-3, the ridge will weaken slightly and this will slow down the storm and also let the storm track WNW. Later, by days 4-5 the ridge is expected to strengthen again., and the storm is forecast to accelerate some. The intensity is problematic as although TD Nine will be over very warm SST’s, TD Nine will be experiencing Moderate to Strong vertical shear along with a large SAL to the North and west which should inhibit some of the convection.
Models are having a very hard time trying to get a grasp on the storm so there will be some bias and error – wait a day or two to see what happens at that time.

Satellite image of TD Nine
Satellite image of TD Nine
Wind Shear
Models for TD Nine
Tropical Weather

Invest 91L

This morning an area of some very intense thunderstorms has become better organized and has now been designated as Invest 91L. The NHC has this system at a 60% chance of becoming a tropical depression by Tuesday morning. Satellite loop imagery is indicating that the intense thunderstorm activity and intensity has been increasing. The latest satellite images seem to indicate that 91L has very good cyclonic turning and may be beginning to form the surface circulation even though 91L is still within the ITCZ and still to close to the equator. This may be the beginning for 91L to break away from the ITCZ and if so then 91L may be classified as either a tropical depression or tropical storm later today or tonight.

RGB Satellite image
AVN Satellite image

With the SST’s in the area at around 29° centigrade and the SAL to the north of 91L along with the wind shear at 10-20 knots, further development is a distinct possibility. The only negatives for any development for 91L is the MJO, which favors downward motion over the tropical Atlantic and as stated earlier, being to close to the Equator.

Later in the week, as 91L approaches the Lesser Antilles, a strong upper-level low near Puerto Rico is forecast to bring high levels of wind shear. This would hamper any quick intensification. As usual, any long range forecasts will have changes so to state where and how strong any system will be is just speculation.

Steering layer forecasts to keep 91L on a WNW track at least for the next 1-2 days, after that a WNW – NW motion is forecast. All those in the Leeward Islands should keep a eye on 91L.

Wind Shear
8am models
Science Tropical Weather

Invests 97L & 98L

The tropics are now heating up and becoming active.

An area in the BOC(Bay of Campeche) has become designated as Invest 98L. The satellite image does show an organizing system with very large amounts of convection along with an anticyclone over it. This also has SST’s of 28° Celcius and the anticyclone it is providing a very good outflow. 98L may have the potential to become Tropical Storm Bonnie. Invest 97L is not as organized as 98L due to moderate amounts of shear and dry air. 98L is currently heading NW-WNW and possibly inland within 72 hours.

Invest 98L


As mentioned – 97L is having problems trying to organize. The data from the NOAA Gulfstream IV jet took samples of the enviroment around 97L and it indicated that the upper-level winds were not conducive for development at least for the moment. The enviroment will probably be changing and within 24-36 hours shear may relax as the upper level low to the north west will be retrograding to the west allowing for a better chance for 97L to develop. In fact, during the day today 97L looked like it was trying to develop a LLC(Low Level Circulation) but all the convection to the right side of the “LLC” was being sheared. The quadrants to the the south and west had no convection due to the dry air and shear. Dry air in the image below is the darker area.

Water Vapor & Dry Air Image

Models seem to indicate that 97L will probably in the South Florida area, at least as Tropical Depression or posssibly as a Tropical Storm. Hurricane development is not indicated at this time.