Assuming the Worst: TD4 becomes Hurricane Danny

18 08 2015

Dale C. S. Destin |

Official_Track_ForecastThe first tropical cyclone (generic term for tropical depressions, storm and hurricanes) to threaten the Caribbean formed this morning. The tropical disturbance over the eastern tropical North Atlantic showed enough organization this morning to be upgraded to Tropical Depression Four (TD4).

The TD4official forecast from the U.S. National Hurricane Centre (NHC) has  the system developing into a Tropical Storm (TS) Danny later today and a Category 2 Hurricane by Sunday about 570 miles due east of Martinique and 650 miles east-northeast of Antigua.

ECMWF model

Notwithstanding the official forecast, arguably the most reliable weather model, the European Centre for Medium Range Weather Forecasting (ECMWF) model, does not seem to agree with it. The ECMWF model was quite early in forecasting the system becoming a TD but at most, so far, only gives it a 40 percent chance of becoming a tropical storm and less than 5 percent chance of becoming a hurricane.

Further, the ECMWF gives the system a less than 5 percent chance of impacting the Caribbean as a TS.

The ECMWF model seems to be expecting the abundance of dry air coming off of Africa and perhaps the return of hostile upper level winds to inhibit the TD.

At this time, I would like to view the Official forecast as nearing the worst case scenario and the ECMWF version of events to be nearing the best case scenario. I could be well wrong; however, given the impeccable track record of the European Centre model, it is difficult to accept that it could be is soo far off its game. It would be an unpleasant surprise to me and many.

Assuming the official forecast to be the more accurate, what would this mean for the Antigua and the Caribbean? We (the Caribbean) would need to prepare for a Category 2 hurricane with winds near 100 mph by Sunday with time to either strengthen further or weaken.

What is expected to be Hurricane Danny by then could impact islands as far south as Trinidad and Tobago or missing all the islands, passing a safe distance northeast of Antigua and Barbuda.

aal96_2015081806_track_gfs

aal96_2015081812_track_early

aal96_2015081812_intensity_earlyAt this time, residents in the Eastern Caribbean should at least be monitoring the potential Hurricane Danny and finalize their hurricane plans. If this goes according to the U.S. NHC forecast, a hurricane watch may be required for portions of the islands around Saturday with a warning around Sunday.

Again, assuming the worst case scenario, parts of the Eastern Caribbean could be in Hurricane Danny around Monday/Tuesday with the most likely path, according to the ECMWF and the U.S. Global Forecasting System (GFS) models, taking it across the northeast Caribbean passing in the vicinity of the Norther Windward Islands, the Leeward Islands, the Virgin Islands and Puerto Rico.

The system has the potential of producing destructive hurricane winds, stronger than those of Gonzalo of last year; flooding rainfall of two to six inches (51-153 mm), rough seas in excess of 12 feet (3.5 metres), significant storm surge flooding, and we cannot rule out tornadoes.

If we were to return to the forecast from the ECMWF as the best case scenario, the system would, at most, become a marginal tropical storm and bring needed rainfall to the Caribbean. Either way, some actions will likely be required this weekend to protect, life, property and livelihood due to hazards brought on by a TC Danny.

A lot can happen over the next several days; it is going to be interesting to see how things pan out; follow us and keep informed.

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Weather Expectations from the Present Disturbance

28 10 2014

Dale C. S. Destin |

Disturbance

Disturbance

A weather disturbance has developed around 250 miles east of Antigua. It has a 20% chance of becoming a tropical cyclone (the generic term for depressions, storms and hurricanes) while it is in our area and a 30% chance of become a tropical cyclone after it moves away for the northeast Caribbean. However, this system is not expected to become a tropical cyclone as the winds aloft are not favourable for much further development. Notwithstanding, based on data available up to this morning, there are three weather scenarios looked at below with respect to the impact of the disturbance on Antigua and the northeast Leeward Islands.

Expected

The weather expected from this disturbance is: Cloudy to overcast skies with precipitation (rain and showers); thunderstorms are likely Tuesday night and Wednesday. Further rainfall accumulation of 10 to 25 mm is possible. The winds are going to swing to the southeast at 5 to 12 knots by tonight. The seas will get up to near two (2) metres or 6 feet tonight and will fall back to near 1.5 metres or 5 feet tomorrow Wednesday.

Best Case

For a best case scenario, the disturbance will get decimated by the unfavourable winds aloft. Thus, although cloudy skies will continue, not much more rainfall will take place.

Isaias_Intensity

Worst Case

For the worst case scenario, the disturbance could develop further and impact Antigua and Barbuda as a tropical depression and the rest of the northeast Caribbean as a minimal tropical storm (Isaias). This scenario is very unlikely; however, if this pans out, quick action would be required to protect life and property.

Isaias_Invest

Conclusion

Changes will definitely take place with this disturbance over the next 24 hours; however, something close to the best case scenario is anticipated. Notwithstanding, this system will be monitored and if the chance of development into a tropical cyclone rises to above 50%, a tropical cyclone alert will be issued by the Antigua and Barbuda Met Service. Residents in the Leeward Islands should continue to monitor this system until it has dissipated or out of our area.





The Atlantic Hurricane Season Consensus Forecast – Aug 14, 2013

14 08 2013

| Dale C. S. Destin

The general consensus among tropical cyclone experts continues to be for an above normal Atlantic Hurricane Season for 2013. The consensus forecast calls for 17 named storms, 8 hurricanes and 4 major hurricanes. A normal season averages of 12.1 named storms, 6.4 hurricanes and 2.7 major hurricanes (See table 1).  Much of the science behind the outlook is rooted in the analysis and prediction of current and future global climate patterns as compared to previous seasons with similar conditions. For this season, the experts are citing a warmer than normal Tropical North Atlantic as the main reason for an above normal season prediction.

Hurricane Season Outlook

What does this mean for Antigua and Barbuda?

 Although there have been great advancements in the science of tropical cyclone (depression, tropical storm and hurricane), the science has not yet reached the stage where accurate predictions can be made of how many cyclones will form in a given year. Also, the science cannot accurately predict when and where these systems will move or make landfall months in advance. The details of the large-scale weather patterns that direct the path of these cyclones cannot be predicted more than a few days into the future. However, for the current active era (1995 – present), there is around a 32% chance or 3 in 10 chances of one or more hurricanes affecting Antigua (directly or indirectly) over the period August – October; this is 4% above the long term chance (1981 – 2010).

The 2013 Hurricane Season

The 2013 Atlantic Hurricane Season, thus far, have produced four (4) named storms. The strongest tropical cyclone for the season has been Tropical Storm Andrea with peak winds of 65 mph and minimum pressure of 992 mb. There has been no hurricane, thus far. Relative to Antigua and Barbuda, Chantal, during it passage through the Eastern Caribbean, spawned a destructive water spout, which impacted Camp Blizzard, Antigua. The hurricane season officially runs from June 1 through November 30 each year; however, tropical cyclones can and have occurred outside the season. The peak of the hurricane season is mid August to late October while the peak of the hurricane season for Antigua is mid August to late September (graph 1).

It Only Takes One

Regardless of the numbers, we should always approach the hurricane season in the same manner each year: be aware and be prepared. The prevention of the loss of life and property from tropical cyclones is a responsibility that should be shared by all. As a reminder, recall our lesson from Hurricane George of 1998: it only takes one hurricane to make it a bad season. Accordingly, the Meteorological Service will play its usual role in alerting the public of any tropical cyclone that may form and threaten Antigua and Barbuda, the Leeward Islands and the British Virgin Islands. We endeavour to provide weather and climate information for the protect life, property, livelihood and the enhancement of the economy – be prepared!

AnuStorms

Graph 1: Antiguan Tropical Cyclones – distribution of tropical cyclones within 120 statute miles of Antiguan (1851 – 2012)

For more information see the links below or email me at dale_destin@yahoo.com. You are also welcome to follow us via twitter facebook youtube and blog .

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References

Accuweather.com, State College, Atlantic Hurricane Season: Three US Landfalls Predicted [online]
<http://www.accuweather.com/en/weather-news/atlantic-hurricane-forecast-2013/12116274>
[Accessed 3 June, 2013]

Colorado State University, Fort Collins, Forecast of Atlantic Seasonal Hurricane Activity and Landfall Strike Probability for 2013 [online].
<http://typhoon.atmos.colostate.edu/Forecasts/2013/aug2013/aug2013.pdf>
[Accessed 12 August, 2013]

Florida State University, Raleigh, FSU COAP Atlantic Hurricane Season Forecast [online]. Available from:
<http://coaps.fsu.edu/hurricanes>
[Accessed 3 June, 2013]

National Oceanic and Atmospheric Administration, Silver Spring, NOAA: Atlantic hurricane season on track to be above-normal [online]. Available from: <http://www.noaanews.noaa.gov/stories2013/20130808_atlantichurricaneupdate.html>
[Accessed 12 Aug, 2013]

North Carolina State University, Raleigh, 2013 Atlantic Tropical Cyclone Outlook [online]. Available from: <http://cfdl.meas.ncsu.edu/research/TCoutlook_2013.html>%5BAccessed 28 May, 2013]

Tropical Storm Risk, London, August Forecast Update for Atlantic and U.S. Hurricane Activity in 2013 [online]. Available from: <http://www.tropicalstormrisk.com/docs/TSRATLForecastAug2013.pdf>
[Accessed 12 Aug, 2013]

United Kingdom Met Office, Exeter, Seasonal Forecasting of Storms [online]. Available from:
< http://www.metoffice.gov.uk/weather/tropicalcyclone/seasonal/forecasting-method&gt;
[Accessed 3 June, 2013]








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