Tag Archives: Cone of Uncertainty

Tropical Cyclone PAULA

For most of what has transpired of the 2010 Atlantic hurricane season we have seen the Caribbean, really a whole region from northern Colombia and Venezuela, through Central America, to southern Mexico, including all of the adjacent eastern Pacific and the southern Gulf of Mexico, close to the boiling point as the atmosphere-ocean environment has been continuously fed by high humidity, an unending supply of rain cells and thunderstorms and regular pulses of tropical waves generated over equatorial Africa, which keep finding their way to “Hurricane Alley’ in the Atlantic as they move westward toward the Lesser Antilles and the Caribbean beyond.

Satellite view of 11 October 2010 showing tropical storm PAULA over the Bay of Honduras moving toward the northwest and Belize/Quintana Roo, with sustained 65 mph winds and plenty of rain and thunderstorms.

  In less than four weeks we’ve seen tropical cyclones Karl, then Matthew and Now Paula emerge from tropical waves in the Caribbean and ‘explode’ near the region of Cape ‘Gracias a Dios’ near the Nicaragua-Honduras border, to then move beyond toward Belize and the state of Quintana Roo in Mexico and neighboring areas. Forecasting these cyclones, which have been generated so close to the landmass of Central America has been difficult, especially as they have moved generally toward the northwest and have come under the influence of frontal weather systems and areas of high pressure and dry air that have moved toward the Gulf of Mexico. This has been reflected in the so-called ‘cone of uncertainty’ in the projections issued by the National Hurricane Center.

Satellite view showing water vapor in the atmosphere, which helps visualize the various external factors affecting tropical storm PAULA as it moves over the northwestern Caribbean.

Currently tropical storm Paula is in the Bay of Honduras moving generally northwest toward Quintana Roo, with sustained winds of 65 mph drawing moisture from as far as the eastern Pacific near Panama and Costa Rica to the Florida straits. The storm is moving in an environment of warm water and humid air that is conducive to further strengthening making it highly likely that PAULA may become a hurricane in the next 18 – 30 hours.

Looking beyond the Caribbean we see a ridge of high pressure over Kansas/Texas/Oklahoma moving generally south and another one over the Carolinas moving toward the east by southeast, which have combine to effectively create a ‘barrier’ ahead of the projected track for tropical storm Paula increasing the difficulty in forecasting what could happen with this cyclone 48 – 72 hours from now. This difficulty is reflected in the must recent forecast, which shows a “circle of uncertainty’  

Track forecast for tropical storm Paula by the Navy Research Laboratory on 11 October 2010 at 1800 EST. Notice how the uncertainty in forecasting what wil happen with this tropical cyclone is reflected in a 'circle' of uncertainty rather than the 'cone' of uncertainty we regularly see.

 rather than a cone centered somewhere in the northwestern Caribbean off the coast of the Yucatan Peninsula, and a tropical storm and quite possibly hurricane Paula meandering and possibly backtracking over the Caribbean. Does this mean the cyclone will remain over water and never make landfall? Or that it may actually strike the coastal region of Quintana Roo? What happens as the storm meanders over the northwestern Caribbean and the dome of high pressure over the Carolinas moves farther east? Would this actually ‘pull’ Paula toward the northeast and Cuba, the Bahamas or even Florida? Or will the system downgrade to just a big area of thunderstorms and rain and eventually dissipate? What happens if one of the tropical waves now in Hurricane Alley enters the Caribbean and begins to influence Paula 3 -4 days from now? The uncertainty of forecasting in certainly evident with Paula.

Such forecasting uncertainty also illustrates the dilemma faced by emergency managers and civil defense authorities in those countries around the Caribbean basin and beyond, which might be in the future track of Paula. With so much uncertainty how do coastal communities that may be impacted by Paula prepare? What do they prepare for, extreme rain, wind, storm surge, a combination of all or none of the above? For coastal regions in Honduras, Guatemala, Belize and Quintana Roo there is no time to waste, as some of them are already beginning to feel the impact of Paula.

Composite of several satellite views on 11 October 2010 shows the Caribbean, Hurricane Alley, equatorial Africa and beyond. Water vapor in the atmsphere makes it easy to see not only tropical storm Paula, but also the several tropical waves just to the north of the equator that are marching westward over equatorial Africa and the still warm waters of the Atlantic.

Looking toward the east over Hurricane Alley and equatorial Africa numerous tropical waves can be seen moving in the general direction of the Caribbean, just as we have seen for most of the current hurricane season. The only noticeable change in this process is that the train of tropical waves appears to have shifted shlightly toward a more southerly route, and the density and size of the tropical waves appears to be diminishing. There also appears to be less moisture in the atmosphere around Central America and the adjecent eastern Pacific as well as the eastern Caribbean than we had seen just a couple of weeks ago, possibly in response to the onset of autumn in the northern hemisphere.

Full-disk view of Earth's western hemisphere on 11 October 2010. The 'belt' of tropical activity continues to circle the globe just above the equator.

MATTHEW: THE UNCERTAINTY OF FORECASTING

Satellite view of Tropical Storm MATTHEW in the early morning of 24 September 2010 as the system continued tracking along a route of 280 N, as it approached the landmass of Central America.

  This morning, 24 September 2010 at 0500 EST, Tropical Storm Matthew was located at LAT 79.8W LON 14.3N still moving generally to the west (approximately 10 degrees north of due west) at 16 mph (25.6 kph) with sustained 50 mph (80 kph) winds and higher gusts, generating large amounts of extreme rain mainly to the west of the center of circulation. By staying on this track during the night Matthew has not only gotten closer to the landmass of Central America increasing the probability of making landfall somewhere near the Nicaragua-Honduras border, but if also has in effect “forced” the models used by the National Hurricane Center (NHC) to “rethink” the projected track. As the storms develops further in the next 12 hours or so, it is entirely possible that new adjustments will be made to the projected track for Tropical Storm Matthew.

Latest forecast track for Tropical Storm MATTHEW developed by the Navy Research Laboratory on 24 September 2010, based on data from NOAA National Hurricane Center. Notice the large level of uncertainty as the projected track moves up the Yucatan peninsula 48 - 72 hours from now.

  Matthew’s latest projected track, based on the consensus of the various models and the interpretation and judgement of NHC’s experts, has the system making landfall as a moderate tropical storm somewhere near Cape Gracias a Dios in the Nicaragua/Honduras border, penetrating into Honduras along the northern coast to then emerge over the waters of the Gulf of Honduras to make a second landfall, this time in southern Belize as a moderate to minor tropical storm. Models then have the storm veer toward the north traversing the Yucatan peninsula near the border between Campeche and Quintana Roo states far away from coastal urban centers in both states, including the tourist resorts in the Mayan Riviera and Cancun. Under this scenario it appears that the storm will weaken considerably while over land or possibly dissipate, however there remains a possibility that the remnants of the storm may emerge over the warm waters of the Gulf of Mexico to reorganize and even re-curb toward the northeast threatening Florida toward the end of next week.

Five-day projected track for Tropical Storm MATTHEW from the NHC on 24 September 2010 at 0800 EST.

Clearly this is a vastly different scenario from the one we had last night, which projected a tropical storm flowing directly into the Gulf of Honduras to strengthen to category 1 hurricane force before making landfall in northern Belize to then attack Chetumal and the coastal region of Quintana Roo state to eventually emerge over the Gulf and re-curb toward central Florida. This illustrates the tremendous challenge faced by NHC forecasters who need to input parameters into the models to initialize and feed models, which at best produce simplified idealized models of the very complex and interactive natural processes taking place in the coupled atmosphere-ocean-land environment.

In the case of Matthew  even though the large aggregation of storm cells and rain was identified as it congealed to the east of the Lesser Antilles 4 – 5 days ago triggering constant monitoring by the NHC, it was only early yesterday that initial rotation started and a central point (a “proto-eye”) of low pressure was identified allowing the model to get a fix on a starting point from which to project future movement. At the same time numerous other parameters, including meteorological factors from the western and central USA, as well as over Central America, the Eastern Pacific and the Caribbean, had to be taken into account to provide parameters for the models. In summary, before yesterday we could only “guesstimate” where this cyclone would go, and even now that the models are working with plenty of data the level of uncertainty especially beyond the next 48 hours remains quite large, to the point where the so-called “cone of uncertainty” resembles a huge balloon once the projected track gets over the Yucatan Peninsula, which means the margin of error is quite large.

However it must be recognized that the NHC capability to accurately forecast the movement  of tropical cyclones has improved significantly in the past 25 years. Certainly the performance with previous storms this year and in recent Atlantic hurricane seasons has been quite good, a true testimony to the experience and accumulated expertize of the professionals who serve at the NHC.