May 26, 2008
Hurricane timeline: Counting down the hours
Excellent summary of a hurricane's life cycle from the Herald Tribune:
Tropical cyclone is the meteorological term for a storm system characterized by a low-pressure center and thunderstorms, producing strong wind and flooding rain. Tropical cyclones form over warm waters from pre-existing disturbances. These disturbances typically emerge every three or four days from the coast of Africa as tropical waves that consist of areas of unsettled weather. Tropical cyclones can also form from the trailing ends of cold fronts and from upper-level lows.
In the Atlantic Basin, tropical cyclones are called hurricanes and must have at least three conditions to form: A pre-existing disturbance with thunderstorms; warm (at least 80 degree) ocean temperatures to a depth of about 150 feet; and light upper level winds that do not change much in direction and speed throughout the depth of the atmosphere.
If weather and ocean conditions continue to be favorable, the system can strengthen first to a tropical depression, tropical storm and then a hurricane.
Every hurricane is different and there are many factors that contribute to its development. However, the following is a general sequence of events that could occur during the development of a Category 2 hurricane (wind speed 96-110 mph) approaching a coastal area.
96 hours before landfall
At first there aren't any apparent signs of a storm. The barometer is steady, winds are light and variable, and fair-weather cumulus clouds appear.
72 hours
Little has changed, except that the swell on the ocean surface has increased to about six feet and the waves come in every nine seconds. This means that the storm, far over the horizon, is approaching.
48 hours
The sky is now clear of clouds, the barometer is steady, and the wind is almost calm.
The swell is now about nine feet and coming in every eight seconds.
36 hours
The first signs of the storm appear. The barometer is falling slightly, the wind is around 11 mph, and the ocean swell is about 13 feet and coming in seven seconds apart. On the horizon, a large mass of white cirrus clouds appear.
As the veil of clouds approaches, it covers more of the horizon.
A hurricane watch is issued, and areas with long evacuation times are given the order to begin.
30 hours
The sky is covered by a high overcast. The barometer is falling at .1 millibar per hour; winds pick up to about 23 mph.
The ocean swell, coming in five seconds apart, is beginning to be obscured by wind-driven waves, and small whitecaps begin to appear on the ocean surface.
24 hours
Small low clouds appear overhead. The barometer is falling by .2 millibars per hour, the wind picks up to 34 mph. The wind driven waves are covered in whitecaps, and streaks of foam begin to ride over the surface. Evacuations should be completed and final preparations made by this time. A hurricane warning is issued, and people living in low-lying areas and in mobile homes are ordered to evacuate.
18 hours
The low clouds are thicker and bring driving rain squalls with gusty winds. The barometer is steadily falling at half a millibar per hour and the winds are whistling by at 46 mph. It is hard to stand against the wind.
12 hours
The rain squalls are more frequent and the winds don't diminish after they depart. The cloud ceiling is getting lower, and the barometer is falling at 1 millibar per hour. The wind is howling at hurricane force at 74 mph. The sea advances with every storm wave that crashes ashore, and foam patches.
6 hours
The rain is constant and the 92 mph wind drives it horizontally. The barometer is falling 1.5 millibars per hour, and the storm surge has advanced above the high tide mark. The sea surface is a whitish mass of spray. It is impossible to stand upright outside without bracing yourself.
1 hour
The rain becomes heavier. Low areas inland become flooded. The winds are at 104 mph, and the barometer is falling at 2 millibars per hour. The sea is white with foam and streaks. The storm surge has covered coastal roads and 16 foot waves crash into buildings near the shore.
The eye
Just as the storm reaches its peak, the winds begin to slacken, and the sky starts to brighten. The rain ends abruptly, and the clouds break and blue sky is seen. The barometer continues falling at 3 millibars per hour and the storm surge reaches the furthest inland.
The winds fall to near calm, but the air is uncomfortably warm and humid. Huge walls of cloud appear on every side, brilliant white in the sunlight.
At this point, the barometer stops falling and in a moment begins to rise, soon as fast as it fell. The winds begin to pick up slightly and the clouds on the far side of the eye wall loom overhead.
AFTER THE STORM
1 hour after landfall
The sky darkens and the winds and rain return just as heavy as they were before the eye. The storm surge begins a slow retreat, but waves continue to crash ashore. The barometer is rising at 2 millibars per hour, and the winds top out at 104 mph.
6 hours
The flooding rains continue, but the winds have diminished to 92 mph. The storm surge is retreating and pulling inland debris out to sea.
12 hours
The rain now comes in squalls, and the winds begin to diminish after each squall passes. The cloud ceiling is rising, as is the barometer at 1 millibar per hour. The wind is still howling at near hurricane force at 69 mph, and the ocean is covered with streaks and foam patches. The sea level returns to the high tide mark.
24 hours
The clouds break into smaller fragments and the high overcast is seen again. The barometer is rising by .2 millibars per hour, the wind falls to 34 mph. The surge has fully retreated from land, but the ocean surface is still covered by small whitecaps and large waves.
36 hours
The overcast has broken and the large mass of white cirrus clouds disappears over the horizon. The barometer is rising slightly, the winds are a steady 11 mph.
September 13, 2007
GOES Floater 2
This is the GOES Atlantic Floater 2 Infrared satellite - this image updates every 30 minutes. Refresh your browser for the latest image.
August 17, 2007
SXMCYCLONE
Here is something cool - it's in French but the graphics are universal: http://sxmcyclone.com/
August 16, 2007
GOES East Caribbean Visible Satellite
GOES East Caribbean Visible Satellite (click the image for a larger view)
Caribbean Islands Webcams
We have a page of Caribbean webcams here - you may be able to get a look at local conditions on some of these cams. If anyone knows of other cams we don't have listed please send me an email.
August 14, 2007
Plymouth State Weather Center Dean Tracking Map
Here is a good simple tracking map for Dean from the Plymouth State Weather Center:
Click the map for the latest info.
June 26, 2007
Tropics remain quiet
Not much is happening in the tropics, so now after all the hype we are starting to see some news reports wondering if the forecasters are wrong (again - like they were last year). It is a very peculiar thing - everyone should be happy about the lack of potentially life threatening weather... not trying to cheer it on. The Palm Beach Post has a pretty good section for hurricanes, satellite images, links, etc. - here is a recent article:
So, what's it all mean? Put up the shutters now or start drinking those gallon jugs of water? And what does El Niņo have to do with it?
"Early-season storms have little or nothing to do with peak-of-season activity," said Richard Knapp, a senior forecaster at the National Hurricane Center in Miami.
"Often we've had one June storm and we've had a strong peak season. And we've had Junes without a storm when the peak of the season hasn't been as strong," he said.
June 13, 2007
Crucial hurricane satellite could fail at any time
This doesn't sound good:
IIf the satellite faltered, experts estimate that the accuracy of two-day forecasts could suffer by 10 percent and three-day forecasts by 16 percent, which could translate into miles of coastline and the difference between a city being evacuated or not
"We would go blind. It would be significantly hazardous," said Wayne Sallade, emergency manager in Charlotte County, which was hit hard by Hurricane Charley in 2004.
June 12, 2007
Tropical weather terms
From the National Hurricane Center - definitions of specific tropical weather terms:
Tropical Wave: A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere.
Tropical Depression: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr) or less.
Tropical Storm: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 kt (39 mph or 63 km/hr) to 63 kt (73 mph or 118 km/hr).
Tropical Storm Watch: An announcement for specific coastal areas that tropical storm conditions are possible within 36 hours.
Tropical Storm Warning: A warning that sustained winds within the range of 34 to 63 kt (39 to 73 mph or 63 to 118 km/hr) associated with a tropical cyclone are expected in a specified coastal area within 24 hours or less.
June 6, 2007
Hurricanes in the Dominican Republic
DR1 has a new page up for "Hurricanes in the Dominican Republic" with a lot of good information, advice, and links to other hurricane resources. If you are planning a trip to the DR during hurricane season, their site is a good place to visit.
June 4, 2007
stormCARIB
Gert van Dijken's stormCARIB is a great resource for tropical weather - specifically for first hand accounts and condition reports from a large network of Caribbean islands residents.
Gert has been doing this for years - he is someone who was "blogging" before people had named it or knew what it was. He also keeps the site almost commercial free - it is a labor of love and it shows. This is a site you need to bookmark if you are interested in tropical weather.
May 24, 2006
The Saffir-Simpson Hurricane Scale
The AP has released a very handy explanation of the Saffir-Simpson Hurricane Scale:
The Saffir-Simpson scale of a hurricane's intensity is used to estimate the potential property damage and coastal flooding. The scale is determined by wind speed, since storm surge sizes depend on the slope of the continental shelf.
