FAQ: Tropical Cyclone Climatology
When is hurricane season?
Contributed by Neal Dorst
The Atlantic hurricane season is officially from 1 June to 30 November. There
is nothing magical in these dates, and hurricanes have occurred outside of
these six months, but these dates were selected to encompass over 97% of
tropical activity. The Atlantic basin shows a very peaked season from August
through October, with 78% of the tropical storm days, 87% of the minor
(Saffir-Simpson Scale categories 1 and 2 -
see Subject D1) hurricane days, and 96% of the major (Saffir-Simpson
categories 3, 4 and 5) hurricane days occurring then (
Landsea
1993). Maximum activity is in early to mid September. Once in a few
years there may be a tropical cyclone occurring "out of season" - primarily in
May or December. (For more detailed information, see
Subject G13 - "What is my chance of having a tropical storm or
hurricane strike by each month?")
The Northeast Pacific basin has a broader peak with activity beginning in late
May or early June and going until late October or early November with a peak in
storminess in late August/early September.
The Northwest Pacific basin has tropical cyclones occurring all year round
regularly though there is a distinct minimum in February and the first half of
March. The main season goes from July to November with a peak in late
August/early September.
The North Indian basin has a double peak of activity in May and November though
tropical cyclones are seen from April to December. The severe cyclonic storms
(>33 m/s winds [76 mph]) occur almost exclusively from April to June and
late September to early December.
The Southwest Indian and Australian/Southeast Indian basins have very similar
annual cycles with tropical cyclones beginning in late October/early November,
reaching a double peak in activity - one in mid-January and one in mid-February
to early March, and then ending in May. The Australian/Southeast Indian basin
February lull in activity is a bit more pronounced than the Southwest Indian
basin's lull.
The Australian/Southwest Pacific basin begin with tropical cyclone activity in
late October/early November, reaches a single peak in late February/early
March, and then fades out in early May.
Globally, September is the most active month and May is the least active month.
(Neumann 1993)
How does El Niño-Southern Oscillation affect tropical
cyclone activity around the globe?
Contributed by Chris Landsea
El Niño/Southern Oscillation (ENSO) - During El Niño events (ENSO warm phase),
tropospheric vertical shear is increased inhibiting tropical cyclone genesis
and intensification, primarily by causing the 200 mb (12 km or 8 mi) westerly
winds to be stronger (Gray 1984). La Nina events (ENSO cold phase) enhances
activity. Recently, Tang and Neelin (2004) also identified that changes to the
moist static stability can also contribute toward hurricane changes due to
ENSO, with a drier, more stable environment present during El Nino events.
The Australian/Southwest Pacific shows a pronounced shift back and forth of
tropical cyclone activity with fewer tropical cyclones between 145° and 165°E
and more from 165°E eastward across the South Pacific during El Niño (warm
ENSO) events. There is also a smaller tendency to have the tropical cyclones
originate a bit closer to the equator. The opposite would be true in La Niña
(cold ENSO) events. See papers by
Nicholls (1979),
Revell and Goulter (1986),
Dong (1988), and
Nicholls (1992).
The western portion of the Northeast Pacific basin (140°W to the dateline) has
been suggested to experience more tropical cyclone genesis during the El Niño
year and more tropical cyclones tracking into the sub-region in the year
following an El Niño
(Schroeder and Yu 1995) , but this has not been completely
documented yet.
The Northwest Pacific basin, similar to the Australian/Southwest Pacific basin,
experiences a change in location of tropical cyclones without a total change in
frequency.
Pan (1981),
Chan (1985), and
Lander (1994) detailed that west of 160°E there were reduced
numbers of tropical cyclone genesis with increased formations from 160E to the
dateline during El Niño events. The opposite occurred during La Niña events.
Again there is also the tendency for the tropical cyclones to also form closer
to the equator during El Niño events than average.
The eastern portion of the Northeast Pacific, the Southwest Indian, the
Southeast Indian/Australian, and the North Indian basins have either shown
little or a conflicting ENSO relationship and/or have not been looked at yet in
sufficient detail.
How might global warming change hurricane intensity, frequency, and rainfall ?
Contributed by Chris Landsea
In November 2006, the global community of tropical cyclone researchers and forecasters met at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization in San Jose, Costa Rica. They released a statement on the links between anthropogenic (human-induced) climate change and tropical cyclones, including hurricanes and typhoons. The following is a summary of their report.
- There have been a number of recent high-impact tropical cyclone events around the globe. These include 10 landfalling tropical cyclones in Japan in 2004, five tropical cyclones affecting the Cook Islands in a five-week period in 2005, Cyclone Gafilo in Madagascar in 2004, Cyclone Larry in Australia in 2006, Typhoon Saomai in China in 2006, and the extremely active 2004 and 2005 Atlantic tropical cyclone seasons - including the catastrophic socio-economic impact of Hurricane Katrina.
- Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind-speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases.
Consensus Statements by International Workshop on Tropical Cyclones-VI (IWTC-VI) Participants :
- Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.
- No individual tropical cyclone can be directly attributed to climate change.
- The recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.
- Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades, leading to difficulties in determining accurate trends.
- There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.
- It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.
- There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.
- Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate, there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.
- Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.
- If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase.
You may access a PDF version of the official report at the NOAA web site.
Are we getting stronger and more frequent hurricanes,
typhoons, and tropical cyclones in the last several years?
Contributed by Chris Landsea
Globally, no. However, for the Atlantic basin we have seen an increase in the
number of strong hurricanes since 1995. As can be seen in section E9, we have
had a record 33 hurricanes in the four years of 1995 to 1999 (accurate records
for the Atlantic are thought to begin around 1944). The extreme impacts from
Hurricanes Marilyn (1995), Opal (1995), Fran (1996), Georges (1998) and Mitch
(1998) in the United States and throughout the Caribbean attest to the high
amounts of Atlantic hurricane activity lately.
As discussed in the previous section, it is highly unlikely that global warming
has (or will) contribute to a drastic change in the number or intensity of
hurricanes. We have not observed a long-term increase in the intensity or
frequency of Atlantic hurricanes. Actually, 1991-1994 marked the four quietest
years on record (back to the mid-1940s) with just less than 4 hurricanes per
year. Instead of seeing a long-term trend up or down, we do see a quasi-cyclic
multi-decade regime that alternates between active and quiet phases for major
Atlantic hurricanes on the scale of 25-40 years each (
Gray
1990;
Landsea 1993; Landsea et al. 1996). The quiet decades of
the 1970s to the early 1990s for major Atlantic hurricanes were likely due to
changes in the Atlantic Ocean sea surface temperature structure with cooler
than usual waters in the North Atlantic. The reverse situation of a warm North
Atlantic was present during the active late-1920s through the 1960s
(Gray et al. 1997). It is quite possible that the extreme
activity since 1995 marks the start of another active period that may last a
total of 25-40 years. More research is needed to better understand these
hurricane "cycles."
For the region near Australia (105-160E, south of the equator), Nicholls (1992)
identified a downward trend in the numbers of tropical cyclones, primarily from
the mid-1980s onward. However, a portion of this trend is likely artificial as
the forecasters in the region no longer classify weak systems as "cyclones" if
the systems do not possess the traditional tropical cyclone inner-core
structure, but have the band of maximum winds well-removed from the center
(Nicholls et al. 1998). These changes in methodology around the
mid-1980s have been prompted by improved access to and interpretation of
digital satellite data, the installation of coastal and off-shore radar, and an
increased understanding of the differentiation of tropical cyclones from other
type of tropical weather systems. By considering only the moderate and intense
tropical cyclones, this artificial bias in the cyclone record can be overcome.
Even with the removal of this bias in the weak Australian tropical cyclones
that the frequency of the remaining moderate and strong tropical cyclones has
been reduced substantially over the years 1969/70-1995/96.
Nicholls et al. (1998) attribute the decrease in moderate
cyclones to the occurrence of more frequent El Nino occurrences during the
1980s and 1990s.
For the Northwest Pacific basin,
Chan and Shi (1996) found that both the frequency of typhoons
and the total number of tropical storms and typhoons have been increasing since
about 1980. However, the increase was preceded by a nearly identical magnitude
of decrease from about 1960 to 1980. It is unknown currently what has caused
these decadal-scale changes in the Northwest Pacific typhoons.
For the remaining basins based upon data from the late 1960s onwards, the
Northeast Pacific has experienced a significant upward trend in tropical
cyclone frequency, the North Indian a significant downward trend, and no
appreciable long-term variation was observed in the Southwest Indian and
Southwest Pacific (east of 160E) for the total number of tropical storm
strength cyclones (from
Neumann 1993). However, whether these represent longer term
(> 30 years) or shorter term (on the scale of ten years) variability is
completely unknown because of the lack of a long, reliable record.
Why do tropical cyclones occur primarily in the summer
and autumn?
Contributed by Chris Landsea
As described in
Subject G1, the primary time of year for getting tropical cyclones is
during the summer and autumn: July-October for the Northern Hemisphere and
December-March for the Southern Hemisphere (though there are differences from
basin to basin). The peak in summer/autumn is due to having all of the
necessary ingredients become most fa vorable during this time of year: warm
ocean waters (at least 26°C or 80°F), a tropical atmosphere that can quite
easily kick off convection (i.e. thunderstorms), low vertical shear in the
troposphere, and a substantial amount of large-scale spin available (either
through the monsoon trough or
easterly waves).
While one would intuitively expect tropical cyclones to peak right at the time
of maximum solar radiation (late June for the tropical Northern Hemisphere and
late December for the tropical Southern Hemisphere), it takes several more
weeks for the oceans to reach their warmest temperatures. The atmospheric
circulation in the tropics also reaches its most pronounced (and favorable for
tropical cyclones) at the same time. This time lag of the tropical ocean and
atmospheric circulation is analogous to the daily cycle of surface air
temperatures - they are warmest in mid-afternoon, yet the sun's incident
radiation peaks at noon.
What determines the movement of tropical cyclones?
Contributed by Chris Landsea
Tropical cyclones - to a first approximation - can be thought of as being
steered by the surrounding environmental flow throughout the depth of the
troposphere (from the surface to about 12 km or 8 mi). Dr. Neil Frank, former
director of the U.S. National Hurricane Center, used the analogy that the
movement of hurricanes is like a leaf being steered by the currents in the
stream, except that for a hurricane the stream has no set boundaries.
In the tropical latitudes (typically equatorward of 20°-25°N or S), tropical
cyclones usually move toward the west with a slight poleward component. This is
because there exists an axis of high pressure called the subtropical ridge that
extends east-west poleward of the storm. On the equatorward side of the
subtropical ridge, general easterly winds prevail. However, if the subtropical
ridge is weak - often times due to a trough in the jet stream - the tropical
cyclone may turn poleward and then recurve back toward the east. On the
poleward side of the subtropical ridge, westerly winds prevail thus steering
the tropical cyclone back to the east. These westerly winds are the same ones
that typically bring extratropical cyclones with their cold and warm fronts
from west to east.
Many times it is difficult to tell whether a trough will allow the tropical
cyclone to recurve back out to sea (for those folks on the eastern edges of
continents) or whether the tropical cyclone will continue straight ahead and
make landfall.
For more non-technical information on the movement of tropical cyclones, see
Pielke and Pielke's "Hurricanes: Their Nature and Impacts on Society".
For a more detailed, technical summary on the controls on tropical cyclone
motion, see Elsberry's chapter in
"Global Perspectives on Tropical Cyclones."
Why doesn't the South Atlantic Ocean experience
tropical cyclones?
In March, 2004 a hurricane DID form in the South Atlantic Ocean and made
landfall in Brazil. But this still leaves the question of why hurricanes are so
rare in the South Atlantic. Though many people might speculate that the sea
surface temperatures are too cold, the primary reasons that the South Atlantic
Ocean gets few tropical cyclones are that the tropospheric (near surface to
200mb) vertical wind shear is much too strong and there is typically no
inter-tropical convergence zone (ITCZ) over the ocean (Gray 1968). Without an
ITCZ to provide synoptic vorticity and convergence (i.e. large scale spin and
thunderstorm activity) as well as having strong wind shear, it becomes very
difficult to nearly impossible to have genesis of tropical cyclones.
In addition, the US National Hurricane Center has documented the occurrence of
a strong tropical depression/weak tropical storm that formed off the coast of
Congo in mid-April 1991 (McAdie and Rappaport (1991)). This storm lasted about
five days and drifted toward the west-southwest into the central South
Atlantic. So far, there has not been a systematic study as to the conditions
that accompanied this rare event.
Does an active June and July mean the rest of the
season will be busy too?
Contributed by Stan Goldenberg
Yes and no. The vast majority of Atlantic activity takes place during
August-September-October, the climatological peak months of the hurricane
season. The overall number of named storms (hurricanes) occurring in June and
July (JJ) correlates at an insignificant r = +0.13 (+0.02) versus the whole
season activity. In fact, there is a slight negative relationship between early
season storms (hurricanes) versus late season - August through November - r =
-0.28 (-0.35). Thus, the overall early season activity, be it very active or
quite calm, has little bearing on the season as a whole. These correlations are
based on the years 1944-1994.
However, as shown in (
Goldenberg
2000), if one looks only at the June-July Atlantic tropical storms and
hurricanes occurring south of 22°N and east of 77°W (the eastern portion of the
Main Development Region [MDR] for Atlantic hurricanes), there is a strong
association with activity for the remainder of the year. According to the data
from 1944-1999, total overall Atlantic activity for years that had a tropical
storm or hurricane form in this region during JJ have been at least average and
often times above average. So it could be said that a JJ storm in this region
is pretty much a "sufficient" (though not "necessary") condition for a year to
produce at least average activity. (I.e., Not all years with average to
above-average total overall activity have had a JJ storm in that region, but
almost all years with that type of JJ storm produce average to above-average
activity.) The formation of a storm in this region during June-July is taken
into account when the August updates for the
Bill Gray and
NOAA seasonal forecasts are issued.
Why do hurricanes hit the East coast of the U.S., but
never the West coast?
Contributed by Chris Landsea
Hurricanes form both in the Atlantic basin (i.e. the Atlantic Ocean, Gulf of
Mexico and Caribbean Sea) to the east of the continental U.S. and in the
Northeast Pacific basin to the west of the U.S. However, the ones in the
Northeast Pacific almost never hit the U.S., while the ones in the Atlantic
basin strike the U.S. mainland just less than twice a year on average. There
are two main reasons. The first is that hurricanes tend to move toward the
west-northwest after they form in the tropical and subtropical latitudes. In
the Atlantic, such a motion often brings the hurricane into the vicinity of the
U.S. east coast. In the Northeast Pacific, a west-northwest track takes those
hurricanes farther off-shore, well away from the U.S. west coast. In addition
to the general track, a second factor is the difference in water temperatures
along the U.S. east and west coasts. Along the U.S. east coast, the Gulf Stream
provides a source of warm (> 80 F or 26.5 C) waters to help maintain the
hurricane. However, along the U.S. west coast, the ocean temperatures rarely
get above the lower 70s, even in the midst of summer. Such relatively cool
temperatures are not energetic enough to sustain a hurricane's strength. So for
the occasional Northeast Pacific hurricane that does track back toward the U.S.
west coast, the cooler waters can quickly reduce the strength of the storm.
Recently (Chenoweth and Landsea 2005), it was re-discovered that a hurricane
struck San Diego, California on October 2, 1858. Unprecedented damage was done
in the city and was described as the severest gale ever felt to that date nor
has it been matched or exceeded in severity since. The hurricane force winds at
San Diego are the first and only documented instance of winds of this strength
from a tropical cyclone in the recorded history of the state. While climate
records are incomplete, 1858 may have been an El Nino year, which would have
allowed the hurricane to maintain intensity as it moved north along warmer than
usual waters. Today if a Category 1 hurricane made a direct landfall in either
San Diego or Los Angeles, damage from such a storm would likely be on the order
of a few to several hundred million dollars. The re-discovery of this storm is
relevant to climate change issues and the insurance/emergency management
communities risk assessment of rare and extreme events in the region.
How much lightning occurs in tropical cyclones?
Contributed by Chris Landsea
Surprisingly, not much lightning occurs in the inner core (within about 100 km
or 60 mi) of the tropical cyclone center. Only around a dozen or less
cloud-to-ground strikes per hour occur around the eyewall of the storm, in
strong contrast to an overland mid-latitude mesoscale convective complex which
may be observed to have lightning flash rates of
greater than 1000 per hour
maintained for several hours.
Hurricane Andrew's eyewall had less than 10 strikes per hour from the time it
was over the Bahamas until after it made landfall along Louisiana, with several
hours with no cloud-to-ground lightning at all
(Molinari et al. 1994). However, lightning can be more common in
the outer cores of the storms (beyond around 100 km or 60 mi) with flash rates
on the order of 100s per hour.
This lack of inner core lightning is due to the relative weak nature of the
eyewall thunderstorms. Because of the lack of surface heating over the ocean
ocean and the "warm core" nature of the tropical cyclones, there is less
buoyancy available to support the updrafts. Weaker updrafts lack the
super-cooled water (e.g. water with a temperature less than 0° C or 32° F) that
is crucial in charging up a thunderstorm by the interaction of ice crystals in
the presence of liquid water
(Black and Hallett 1986). The more common outer core lightning
occurs in conjunction with the presence of convectively-active rainbands
(Samsury and Orville 1994).
One of the exciting possibilities that recent lightning studies have suggested
is that changes in the inner core strikes - though the number of strikes is
usually quite low - may provide a useful forecast tool for intensification of
tropical cyclones.
Black (1975) suggested that bursts of inner core convection
which are accompanied by increases in electrical activity may indicate that the
tropical cyclone will soon commence a deepening in intensity. Analyses of
Hurricanes Diana (1984), Florence (1988) and Andrew (1992), as well as an
unnamed tropical storm in 1987 indicate that this is often true
(Lyons and Keen 1994 and
Molinari et al. 1994).
What is the 20th century hurricane record for each U.S.
coastal county?
Contributed by Chris Landsea
The NOAA
Coastal Services Center provides an on-line revision to the original
NOAA technical memorandum by Jarrell et al. 1992. One can query for any U.S.
coastal county and obtain a graph with hurricane strikes and population
changes. This information lets users know how many and how often hurricanes
have struck, what Saffir- Simpson Hurricane Scale category they were, and how
the populations have changed during the 20th Century.
What is my chance of having a tropical storm or
hurricane strike by each month?
Contributed by Chris Landsea
The following figures show that for
at any particular location what the chance that a tropical storm or hurricane
will affect the area sometime during an individual month.
These figures were created by Todd Kimberlain.
We utilized the years
1944 to 1999 in the analysis and counted hits when a storm or hurricane was
within about 100 miles (165 km). Many folks are are concerned about the
possible impacts that a hurricane could have on their vacation. If so, please
check with your hotel, cruise company, etc. to find out how they inform their
guests when a hurricane is coming, what actions they plan and what refund
policies they have (if any). Keep in mind that a direct hit by a major
hurricane is an extremely rare event and if I had a chance - for example - to
go on a cruise in the Caribbean Sea during hurricane season, I would go without
hesitation.
What is my chance of being struck by a tropical storm
or hurricane?
Contributed by Chris Landsea
The figure here shows for any particular location what the chance is that a
tropical storm or hurricane will affect the area sometime during the whole June
to November hurricane season. We utilized the years 1944 to 1999 in the
analysis and counted hits when a storm or hurricane was within about 100 miles
(165 km). This figure is created by Todd Kimberlain.
For example, people living in New Orleans, Louisiana have about a 40% chance
(the green-orange color) per year of experiencing a strike by a tropical storm
or hurricane. For the U.S., the locations that have the highest chances are the
following: Miami, Florida - 48% chance; Cape Hatteras, North Carolina - 48%
chance; and San Juan, Puerto Rico - 42% chance.
For any particular location the chance that a hurricane will directly affect
the area sometime during the whole June to November hurricane season is shown
here. We utilized the years 1944 to 1999 in the analysis and counted
hits when a hurricane was within about 60 miles (110 km). This figure is
created by Todd Kimberlain. (For example, the chance for Miami, Florida is
about 16%.)
For any particular location what the chance is that a major hurricane (Category
3, 4 or 5) will directly affect the area sometime during the whole June to
November hurricane season is shown
here. We utilized the years 1944 to 1999 in the analysis and counted
hits when a hurricane was within about 30 miles (50 km). This figure is created
by Todd Kimberlain. (For example, the chance for Miami, Florida is about 4%.)
Many folks are are concerned about the possible impacts that a hurricane could
have on their vacation. If so, please check with your hotel, cruise company,
etc. to find out how they inform their guests when a hurricane is coming, what
actions they plan and what refund policies they have (if any). Keep in mind
that a direct hit by a major hurricane is an extremely rare event and if I had
a chance - for example - to go on a cruise in the Caribbean Sea during
hurricane season, I would go without hesitation.
What is the average number of tropical storms and
hurricanes to affect my town?
Contributed by Chris Landsea
The figure
here (created by Todd Kimberlain) shows for any particular location
what the average number of tropical storms and hurricanes is that affect the
area sometime during the whole June to November hurricane season. We utilized
the years 1944 to 1997 in the analysis and counted hits when a storm or
hurricane was within about 100 miles (165 km).
What is the peak number of tropical storms and
hurricanes to affect my town?
Contributed by Chris Landsea
The figure
here (created by Todd Kimberlain) shows for any particular location
what the highest number of tropical storms and hurricanes is that affect the
area sometime during the whole June to November hurricane season. Blue
indicates a peak of just 1 storm, orange is 2 storms, brick red is 3 storms,
green is 4 storms and red is 5 storms. We utilized the years 1944 to 1997 in
the analysis and counted hits when a storm or hurricane was within about 100
miles (165 km).
I'm vacationing in the Caribbean/the Bahamas/ Central
America/Miami or elsewhere in the tropics during hurricane season. What's my
chance of getting hit by a hurricane?
Contributed by Chris Landsea
Typically, for someone visiting the tropics during June through November, the
chance to experience (or even be threatened by) a hurricane is very small.
As an example, this figure shows the chances to have a direct hit by a
hurricane during the month of September, which is usually the busiest month. If
we look at Puerto Rico, the chance is 8% of experiencing a hurricane, if you
are there for the WHOLE month. If you are there for, say, only a week, then the
chance would be one fourth of that - or only about 2% chance.
To put this into perspective, if you made 50 one week trips to Puerto Rico in
September, you would only experience a direct hit in ONE of those 50 visits. So
the chances to get impacted by a hurricane are quite small for relatively short
trips. (And the case chosen here is the WORST possible, as all other locations
in all other months have smaller chances of being hit by a hurricane.) If you
would like to see chances of hurricane strikes in other months, see Question G12.
Despite the chance being small, one should know in advance what your hotel's,
cruise company's, etc. policy is for guests when a hurricane is coming, what
actions they plan and what refund policies they have (if any). As is described
above, a direct hit by a hurricane is a very rare event for a short visit and
if I had a chance - for example - to go on a cruise in the Caribbean Sea during
hurricane season, I would go without hesitation.
What is the average forward speed of a hurricane?
Contributed by Neal Dorst
The forward speed of hurricanes is very latitude dependent. Typically, Atlantic hurricanes track along the western side of the subtropical ridge in the western Atlantic. As they recurve (turn more northerly) from their westward track they usually slow down. If they reach the midlatitudes, they can interact with upper-level troughs and pick up speed.
In the table below, the forward speed of hurricanes in the HURDAT database have been averaged in 5 degree latitude bins:
Forward speed of Atlantic hurricanes
averaged by 5 degree latitude bins
Latitude
bin
| Speed
| No.
Cases
|
| km/hr
| knt
| mph
|
| 0°- 5°N | 25.5 | 13.7 | 15.8 | 100
|
| 5°-10°N | 21.8 | 11.8 | 13.6 | 3282
|
| 10°-15°N | 19.6 | 10.6 | 12.2 | 5808
|
| 15°-20°N | 17.7 | 9.5 | 11.0 | 6086
|
| 20°-25°N | 17.7 | 9.5 | 11.0 | 6817
|
| 25°-30°N | 20.1 | 10.9 | 12.5 | 5321
|
| 30°-35°N | 27.6 | 14.9 | 17.2 | 2835
|
| 35°-40°N | 38.5 | 20.8 | 23.9 | 1026
|
| 40°-45°N | 46.7 | 25.2 | 29.0 | 263
|
| 45°-50°N | 51.4 | 27.7 | 32.0 | 36
|
| 50°-55°N | 51.4 | 27.8 | 32.0 | 15
|
| 55°-60°N | 55.8 | 30.1 | 34.7 | 1
|
While there are many cases where the forward speed over the 6 hour interval in the hurricane database is zero, such as Mitch in 1998, the highest speed in the database is for unnamed Tropical Storm #6 in 1961. As it got caught up by a midlatitude trough over the midatlantic states, it went speeding off northeastward over Maine and New Brunswick at a maximum speed of 112.25 km/hr (60.57 knt or 69.75 mph). The fastest hurricane in the record was Emily in 1987, whose maximum speed reached 110.48 km/hr (59.61knt or 68.65 mph) as it raced over the North Atlantic, before it turned extratropical.
Last updated January 16, 2007