Tropical Storm ISAAC

A lot has happened in the northern tropics in the week since we posted an article, in which we indicated 20 August marked the historical “opening” of the peak of the Atlantic hurricane season!

First there was tropical depression seven in the western Caribbean, which traversed portions of Central America and the Yucatan peninsula emerging over the Bay of Campeche, in the southwestern Gulf of Mexico, to become Tropical Storm HELENE, which in turn spawned another tropical wave that on this 21 August lingers just off the eastern coast of Mexico in the western Gulf.

Then there was Hurricane GORDON over the open waters of the Atlantic, which weakened to tropical storm strength before impacting the island of Santa Maria in the Azores, before continuing to lose strength as it entered much cooler waters near northwestern Africa and the Iberian peninsula in southwestern Europe.

Color-enhanced infrared GOES satellite image of 21 August 2012 showing Tropical Storm ISAAC approaching the Lesser Antilles, and other storm activity along Hurricane Alley and the Gulf of Mexico

Next, just like clockwork, one of two tropical waves riding along Hurricane Alley became Tropical Depression #9 and today, 21 August 2012, it became the ninth-named tropical cyclone of the 2012 Atlantic hurricane season under the name of ISAAC, which at 2200 EDT was some 640 km east of Guadeloupe in the Lesser Antilles moving toward the west at 25 kph with maximum winds of 65 kph. Tropical Storm Isaac appeared quite disorganized and ragged as the hour approached 2400 EDT, but it had a large wind-field as it continue moving toward the Lesser Antilles and the Caribbean into an environment of very warm surface waters and atmospheric conditions that may favor further strengthening and cyclonic development over the next 48-72 hours. Following is a five-day forecast track based on the model consensus as of 2000 EDT on 21 August 2012, which places the storm over Cuba and moving toward the Gulf or Western Florida near the end of the 120-hour forecast period. In this regard it should be of interest to note that at least one of the models is forecasting a more westerly track, which takes Isaac toward the Yucatan peninsula and the coast of Quintana Roo in Mexico.

Five-day track for Tropical Storm ISAAC developed by the U.S. Navy Research Laboratory on 21 August 2012 based on data from NOAA

Chasing Isaac along Hurricane Alley is a large tropical wave that at 2200 EDT was located some 650 km South Southwest of the Cape Verde Islands and moving west at more than 30 kph. This particular tropical wave is showing signs or getting better organized and stronger around a cell of low pressure, and as of 2000 EDT this 21 August was given a 70% chance of becoming a tropical cyclone within the next 48 hours by the National Hurricane Center of NOAA.

Color-enhanced infrared NOAA satellite image of 21 August 2012 showing tropical wave activity over the Eastern Atlantic and Equatorial Africa

Still farther to the east, over the eastern Atlantic and the Tropical Wave Assembly Line in Equatorial Africa the generation of storm cells and westerly tracking tropical waves continues in full, raising the probability that still more of these tropical cyclone seedlings may continue to emerge over the eastern Atlantic and into Hurricane Alley over coming days just as as Florida, and the nation, gets ready to commemorate the 20th anniversary of Hurricane Andrew this Friday 24 August.

Half a world away from Florida in that hot spot of cyclogenesis over the Philippines Sea and the South China Sea two tropical cyclones, Typhoon TEMBIN and Typhoon BOLAVEN are menacing Taiwan and China, beyond, in a region that has seen repeated tropical cyclone impacts over the past several weeks. Following are projected five-day tracks for both of these two tropical cyclones.

Five-day track as of 21 August 2012 for Typhoon TEMBIN developed by the U.S. Navy Research Laboratory based on data from NOAA

Five-day track as of 21 August 2012 for Typhoon BOLAVEN developed by the U.S. Navy Research Laboratory base on data from NOAA

As we monitor the progress of the 9th named storm of this 2012 Atlantic hurricane season, as well as other potential tropical cyclones moving into position along Hurricane alley and Equatorial Africa, let us remember that 20 years ago in 1992 by 21 August we had not had a single named storm in the Atlantic basin. Likewise, let us not forget that all it may take is just one hit from a tropical cyclone to cause catastrophic damage, death, injury and unimaginable human suffering. Those of us who went through Hurricane Andrew or worked in its aftermath can certainly attest to that. Pay Attention! Be Prepared! And above all MITIGATE!!

22 AUGUST AT 0500 EDT

Five hours later, Hurricane hunter aircraft reconnaissance and satellite imagery show a slight strengthening and better organization of the storm. Maximum sustained winds are now around 75 kph as Tropical Storm Isaac continues moving toward the Lesser Antilles and the Caribbean beyond. The new five-day track from the U.S. Navy Research  Lab and infrared satellite image are shown below:

Five-day track for Tropical Storm Isaac as of 0500 EDT prepared by the U.S. Navy Research Laboratory based on NOAA observations and data

Infrared NASA satellite image of 22 August as of 0515 EDT showing a better organized system with very cold cloud tops above

Also this early morning, the tropical wave chasing T.S. Isaac down ‘Hurricane Alley’ is showing considerable strengthening over the past five hours and much better organization. Based on most recent observations the National Hurricane Center is giving this system a 90% chance of tropical cyclone formation  in the next 12-24 hours. Visible light satellite imagery from NASA shows a large system with plenty of convection and storms around its center of low pressure, as shown below. In my opinion most indicators from current satellite imagery favor tropical cyclone development for this tropical wave within the next few hours this Wednesday 22 August:

NASA visible light satellite image of 22 August at 0515 EDT showing a strengthening tropical wave chasing Tropical Storm Isaac down Hurricane Alley

All interest in the Caribbean should monitor the progress of both these storms closely over the next few days. For those in the USA, especially in Florida, the possibility of approaching tropical cyclone conditions around the beginning of the week of 27 August exists. Pay attention, be prepared. MITIGATE!

2012 Atlantic Hurricane Season: 40% done!

On this Tuesday 14 August 2012 we are approaching the 20th anniversary of Hurricane Andrew, which devastated Homestead, Florida City and part of Miami the 24th of August 1992 to then continue across the state and the Gulf of Mexico to make a second landfall in Louisiana. Perhaps more importantly, for the 2012 Atlantic hurricane season, we mark 75 days or 40% into the current season as we also approach a 45-day period that historically marks the time of the year when the majority of Atlantic hurricanes form. This means  that 40% of the season is done with, but we are about to enter the period of higher risk relative to potential hurricane impacts. The figure that follows [from NOAA – Historical Climatology Series 6-2: Tropical Cyclones of the North Atlantic Ocean, 1851-2006, Page 24, Figure 8] illustrates how the period from 20 August through 1 October marks the peak of the annual Atlantic hurricane season, based on 137 years of records.

As we approach these important Atlantic hurricane milestones, I thought it would be a good idea to put the 2012 Atlantic Hurricane season in context by taking a look at what is happening now in the worldwide tropics.

For starters the Atlantic basin appears to be rather quiet with no major tropical cyclone activity currently under way. There is a large region of disturbed weather off the eastern coast of Nicaragua and Honduras stemming from the remnants of Tropical Depression #7, which had largely dissipated after crossing from the Atlantic into the Caribbean over this past weekend. This storm is moving generally westward with very little chance of cyclonic development before it crosses overland in central America, where it is expected to generate heavy rains and blustery winds for the remainder of this week.

GOES satellite image [courtesy of NOAA] of 14 August 2012 showing a re-generated Tropical Depression #7 in the Caribbean approaching Central America and several other tropical waves and low-pressure cells around the larger Atlantic basin
Also in the Atlantic basin there is a region of disturbed weather associated with a cell of low pressure some 1,600 kilometers southeast of Bermuda, over the open waters of the Atlantic, moving toward the northwest with a low probability (30%) of tropical cyclone development as the system will move into an atmospheric environment of dryer air and wind shear, although other factors such as the system moving into a much warmer section of the ocean may contribute to an increase in the probability of cyclonic development over the next 48 hours. Beyond this, there are a couple of rather weak tropical waves in Hurricane Alley and other weak and disorganized tropical cells over Equatorial Africa, which currently do not show much in the way of potential for further development over the next couple of days.

Tropical Storm Hector’s track as of 14 August 2012 developed by the U.S. Navy Research Laboratory based on data from NOAA

Over in the northern east Pacific Tropical Storm HECTOR is some 600 kilometers off the Pacific coast of Mexico moving westward at 10 kph with maximum sustained winds of 75 kph and higher gusts. In the same region, to the southeast of T.S. Hector’s current location off the coasts of Central America there are several areas of disturbed weather generating rain and thunderstorms in a feature that has persisted in that region for a few months already in 2012, and for much of the seasons over the last 2 – 3 years.

Track for Tropical Storm KAI-TAI on 14 August 2012 developed by the U.S. Navy Research Laboratory based on data from NOAA

At the other extreme of the Pacific Ocean, over the northwestern Pacific, Tropical Storm KAI-TAI is moving generally northwestward between the Philippines and Taiwan toward landfall in China, following a course recently traveled by other tropical cyclones. To the west of the Philippines and extending for more than 5,000 kilometers into the central Pacific we continue to see a large an elongated mass of disturbed weather, which has been a persistent feature in that region over the past several weeks.

Satellite view of 14 August 2012 [courtesy of NOAA] showing the eastern north Atlantic and the western rage of Equatorial Africa where the ‘Tropical-wave Assembly Line’ now reaches to 20 degrees of latitude North

Rounding-up this overview of current tropical cyclone activity worldwide it is interesting to note that the Tropical-wave Assembly Line over Equatorial Africa has continued its northward drift, and it now reaches to the latitude of 20 degrees North. The Belt of Tropical Activity continues to extend from the Eastern Atlantic to the far western Pacific, while showing particular strength across much of the Pacific.

Full Earth disk satellite view [courtesy of NASA] of 14 August 2012 showing the ‘Belt of Tropical Activity’ extending across much of the Pacific Ocean as well as Tropical Storm HECTOR currently active near the coast of Mexico
Full Earth disk satellite image [courtesy of NASA] of 14 August 2012 showing the western hemisphere and the ‘Belt of Tropical Activity’ extending from the Eastern Atlantic well into the Pacific Ocean
 

A final piece of information to complete this overview relates to the status of sea surface temperatures over the northern Atlantic. From the satellite image and overlay of sea surface temperatures that follow, it is clear most of the northern Atlantic basin has warmed-up considerably over the past few weeks, especially in its eastern region where cooler waters had persisted until recently. This image also shows increasingly warmer waters along ‘Hurricane Alley’ and in the Gulf of Mexico, which provide one of the required components for cyclogenesis as we approach the historical peak of the annual Atlantic hurricane season.

Satellite image of 13 August 2012 [courtesy of NOAA] with an overlay of sea surface temperatures across the northern Atlantic basin showing waters at or above 30 Celsius along ‘Hurricane Alley’ and a good portion of the Gulf of Mexico
 This is what is currently happening in the worldwide tropics in terms of tropical cyclone activity. With almost 2/3 of the year 2012 already gone, it would appear we may be looking at a third consecutive ‘sub-par’ annual worldwide season in terms of tropical cyclone generation. As of 14 August there have been a total of 43 named tropical cyclones worldwide, which is far below the annual worldwide average over the past 50 years or so. We will have to wait and see what happens in what remains of 2012, not only in the Atlantic and the current ‘hot spots’ over the northwestern Pacific, but also in the Southern hemisphere as activity there should start to pick-up again toward the end of the year.

As we get ready to commemorate the 20th anniversary of Hurricane Andrew, and prepare for what the peak of the Atlantic hurricane season may bring in terms of tropical cyclone activity, let us not forget that it only takes one impact by a hurricane, of any category, to cause considerable damage to buildings and property, untold human suffering, and high risk to life. Consequently we must remain alert, always be prepared, and continue to practice hurricane mitigation in order to reduce the potential for damage from recurring hurricane impacts.