Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 10:29 PM GMT on July 09, 2005
Entry from Friday, July 8
Dennis has come ashore on the south coast of Cuba, and it took one of the worst possible landfall trajectories--a 70-mile long track scraping the coast with its right eyewall. The right eyewall contains the hurricane's strongest winds and highest storm surge, and normally only a 5 to 10 mile section of coast suffers it. Cuba just had 70 miles of coast with some of its prime tourist areas suffer a storm surge of at least 13 feet, and probably 20 feet or higher in many places. Add to this the hurricane's sustained winds of 145 - 150 mph, and the result will be a multi-billion dollar destruction of a key part of the island's economy. Dennis has also made a direct hit on Cienfuegos, a city of 200,000, and is now aiming at the Caribbean's largest city, Havana. The destruction occurring in Cuba from this storm must be truly staggering.
Ham radio reports from Cienfuegos indicate that more than 85% of the power lines were down and extensive damage had occurred to the communications infrastructure. Sustained winds of 99 mph and a wind gust of 149 mph was measured in the city at 1:30pm EDT.
Entry from 10am EDT
Yesterday afternoon, Dennis went through an eyewall replacement cycle where the inner eyewall collapsed, and a new eyewall formed with a diameter of about 20 miles. This ended a period of rapid intensification, and the storm stayed roughly constant in intensity as a minimal Category 4 storm (135 mph, 950 mb).
The 8:30am EDT hurricane hunter flight just found a central pressure of 938 mb and winds at 10,000 feet of 155 mph, which means Dennis has recovered from its eyewall replacement cycle, and is now intensifying again. The eye is a healthy 15 miles in diameter, and it is unlikely that another eyewall replacement cycle will happen before the storm hits Cuba tonight. Cuba will probably see Dennis at its peak--and this could very well mean Category 5.
Dennis is now the most intense June or July hurricane on record, beating out Hurricane Audrey of June 1957, which was a Category 4 storm with 145 mph winds and a central pressure of 946 mb at its peak. Audrey killed 390 people in Texas and Louisiana when it came ashore, making it the sixth most deadly U.S. hurricane on record.
Today will be the worst day in Cuba's modern history. Dennis is a worst-case hurricane following a worst-case path for the island. The storm is already punishing Cuba as it moves parallel to the island, subjecting much of the island to hurricane force winds and rainfall totals of 10 - 15 inches, and destroying much of the rich sugar cane fields and other crops. The situation will get much worse tonight when the storm makes landfall, pushing a storm surge of 20 feet or higher onto a long section of the coast. Dennis will pass near Havana, the most heavily populated part of the island. Although loss of life will be low thanks to Cuba's excellent civil defense system, the destruction of buildings will probably be the worst in Cuba's history. Building collapses are common in Cuba without having hurricane winds battering the cities. Dennis will damage or destroy hundreds of thousands of buildings, leaving a large percentage of Cuba's population homeless. Lack of fresh water and electricity will be serious problems, and Cuba's political stability could well be threatened by the scope of what is likely to be its greatest disaster in modern history.
On that cheerful note, let's talk about the plight of the poor people living in Florida's panhandle, which is likely to bear the brunt of yet another major U.S. landfalling hurricane. Dennis will cross Cuba over a realtively flat section of the island, and be reduced in intensity to only a Category 3 or weak Category 4. Once over the Gulf, some intensification is likely, but the amount remains uncertain. The waters get cooler further north, and since we are still early in July, the depth of warm waters is limited. Dennis may stir up enough cool waters from down deep to limit intensification to a Category 4, or perhaps even reduce it to a Category 2. Dennis looks likely to hit within 50 miles of where last year's Category 3 Hurricane Ivan hit, killing 25 and causing $7 billion in damage. Expect a repeat of this performance, although the exact strength of Dennis at landfall could range between Category 2 and Category 4, and will greatly influence how much damage is done. Key West will likely get hurricane force winds tonight, but miss a direct hit by 40 or so miles. The outer bands of Dennis are already affecting the island; a squall with heavy rain and winds to 30 mph passed through the island at 8:30am. The rest of the west coast of Florida is also likely to miss a direct hit, but still get tropical storm force winds of about 40 mph.
Entry from Thursday, July 7
At 3:55pm EDT, the hurricane hunters sent in an eye report of a central pressure of 957 mb, 1mb higher than the previous hour's report. They also reported the eyewall was beginning to break up, with an elliptical shape 9 x 6 nm, and open to the south. Satellite pictures also show the disintegration of the inner eyewall, and the storm should begin a slow weakening period that will last a day or so. It should maintain Category 3 strength until it hits Cuba. NHC is forecasting Dennis to continue intensifying the next 12 hours, which I believe means the winds will continue to come up into equilibrium with the rapid pressure drop we saw. I wouldn't expect much in the way of pressure falls until tomorrow, when the eyewall can re-establish itself.
Entry from 1 hour ago:
At 2:30pm EDT, the hurricane hunters sent in an eye report of a central pressure of 956 mb--an impressive 6 mb drop in just 70 minutes! The eye diameter was a tiny 9 nm (10.5 miles), and the storm is undergoing the rapid shrinkage of the eye and sudden deepening characteristic of an eyewall replacement cycle. I expect that within a few hours, the winds will respond to the sudden pressure drop, and Dennis will be a major Category 3 hurricane, and may make it to Category 4 status (135 mph winds) before the inner eyewall collapses and the storm starts weakening slightly. Dennis will not reach Category 5 status today, though--the pressure would have to be much lower than 956 mb at the beginning of an eyewall replacement cycle to achieve Category 5 status. Nevertheless, Hurricane Dennis has grown into an impressive Cape Verdes-type hurricane, and will be a serious threat to everything in its path. After blasting Haiti and Jamaica, Dennis's next targets will be the Cayman Islands and Cuba--and then the Florida Keys. Today, I will focus on the Caymans, Cuba, and the Florida Keys. Tomorrow--it's time to talk about the mainland U.S.
Florida emergency management officials have ordered a mandatory visitor and nonresident evacuation for the entire Florida Keys beginning at noon Thursday. At 6 pm, all residents of mobile homes are required to evacuate. The rest of the residents of the Keys have not been ordered to evacuate, but likely will be asked to do so Friday. With only one road out of the Keys, this part of the U.S. has the longest lead evacuation time--a full 72 hours is needed to evactuate the entire island chain. Last year, Hurricane Ivan prompted a mandatory evacuation order as well, and 30,00 - 60,000 of the 80,000 residents of the Keys heeded the order. The Keys escaped serious damage from Ivan, and no doubt many Keys residents will try their luck and ignore the evacuation order for Dennis. Like Jamaica and New Orleans, the Keys have had an inordinate amount of luck dodging direct hits from major hurricanes. I think their luck will hold this time around, too, but one of these days, those residents who ignore the evacuation order will wish they hadn't!
Grand Cayman Island is still years away from recovery from last year's Hurricane Ivan, which brought sustained winds of 150 mph, gusts to 170 mph, and a storm surge of 10 - 12'. 95% of all the buildings on the island were damaged or destroyed. Grand Cayman will likely escape the brunt of Dennis, but its sister islands Little Cayman and Cayman Brac, which lie 150 km to the east-northeast, may feel the storm's full force. Cayman Brac escaped Hurricane Ivan's rampage with minimal damage--winds only reached 50 mph there--but Dennis may bring winds of over 100 mph. Loss of life on Cayman Brac is unlikely, though, since the island's population of 1300 generally takes shelter in a large network of natural caves on the west end of the island that provide ideal hurricane protection. Cayman Brac's reefs--ranked by diving enthusiasts as some of the best in the world--are unlikely to be seriously harmed by Hurricane Dennis, though. Ivan, a much stronger storm, did only minimal damage to the reefs near Grand Cayman Island, and did divers a favor by clearing out old algae deposits and opening up new holes in coral walls for divers to explore.
After whipping the Cayman Islands, Dennis will likey hit western Cuba. This is the same region that was struck by Hurricane Charley on Friday, August 13, 2004 (Fidel Castro's 78th birthday). Charley was a Category 3 storm, with sustained winds of 120 mph and a storm surge of 13 feet when it hit Cuba, passing just 15 miles west of Havana. Charley did over $1 billion in damage to Cuba, and damaged or destroyed over 70,000 buildings. The 13 foot storm surge on the coast south of Havana was particularly devastating. For example, the fishing village of El Cajio on Cuba's south shore lost 290 of its 300 homes to the storm surge.
Charley caused serious problems in Havana and the surrounding areas. 70% of Havana's two million residents had no fresh water four days after the storm, and more than half had no power 2 weeks after the storm. The Cuban government shut down the entire electrical grid in the hours prior to Charley's arrival to prevent damage from power surges and intermittent service, or else the damage to the power grid would have been far worse.
Unfortunately for Cuba, Dennis is likely to bring a replay of the miseries brough by Charley. A storm surge of 12 - 14 feet is likely once again, and since the storm is travelling at more oblique angle to the coast than Charley did, the area of Cuba likely to be seriously affected by hurricane is much greater. Dennis will be another billion dollar hurricane for Cuba, and probably the second most destructive hurricane ever to hit the island, behind 2001's Category 4 Hurricane Michelle, which damaged or destroyed over 110,000 buildings. But thanks to Cuba's phenomenal civil defense plans, loss of life is likely to be low. Only five Cubans died in Hurricane Michelle, and four in Hurricane Charley.
Entry from Wednesday, July 6
Dennis is steadily intensifying, and will likely affect the islands of Hispanolia, Jamaica, and Cuba as a Category 1 or 2 hurricane before coming ashore in the U.S.--who knows where? Since it is way too early to speculate on where in the U.S. Dennis might hit, let's focus on which island will bear the brunt of the storm.
The latest computer model guidance is tightly clustered, bringing Dennis between Jamaica and Hispanolia on Thursday. Dennis could potentially hit either island as a Category 1, 2, or 3 hurricane. Let's consider Jamaica first. In 2004, Category 4 Hurricane Ivan was headed straight for Jamaica, and in the final hours just before landfall, made a sudden jog to the south around the island, largely sparing it from massive destruction. The track looked so suspicious, I suspected at the time that Jamaica somehow deflected the storm by creating some sort of alteration of the steering currents of the hurricane. I couldn't think of a very good mechanism for how this might have happened, though, since Jamaica is a small island, and the tallest mountains on the island are only 7,000 feet high. Steering currents for a hurricane operate at much higher altitudes, centered at an altitude of perhaps 25,000 feet. When I used NOAA's excellent Hurricane Tracking Tool to plot up all Category 2 or higher hurricanes for the past 150 years that passed within 75 miles of Kingston, Jamaica, it revealed that Ivan was the only storm that made a sudden jog around Jamaica, and that in general, hurricanes just ignore the island and blast right over it.
So, don't be surprised if Dennis rips straight across Jamaica like Hurricane Gilbert did in 1988. However, Jamaica is heavily forested and able to handle extreme hurricane rains without major loss of life; furthermore, the hurricane storm surge is usually not a problem, since the storm surge wave can just wrap aorund the island without being forced up on shore. The primary hazard to people are the winds, which easily destroy the tin shacks much of the poor populace live in, but usually don't cause heavy loss of life. A direct hit by Dennis will cause a lot of damage but not much loss of life on Jamaica.
Of greater concern is Haiti. A direct hit by even a Category 1 Hurricane Dennis could easily kill thousands on island, and even a side-swipe could well kill hundreds. The problem on Haiti is that they have chopped down 98.4% of all their trees, leaving the denuded mountains unable to absorb heavy rains. Heavy hurricane rains wash down the mountainsides, sweeping the helpless Haitians to their doom. Last year's Hurricane Jeanne--just a tropical storm when it hit Haiti--killed over 3000 Haitians, making it the 12th most deadly hurricane ever. Dennis' current projected path has it sideswiping Haiti's western tip, which is less populated than the areas of the island that usually suffer extreme devestation, so I am hopeful that Dennis will cause minimal loss of life in Haiti.
Entry from Tuesday, July 5
The newly-formed Tropical Storm Dennis over the eastern Carribbean looks poised to become Hurricane Dennis later this week. The storm has a typical look of a classic Cape Verdes-type hurricane at its formative stages. It has a large circulation covering most of the eastern Caribbeam, plenty of deep convection near the center, spiraling bands of low-level cumulus wrapping into the center, and a decent upper-level outflow pattern of high cirrus clouds. The storm is over warm ocean waters >28C and has a favorable environment with light shear ahead of it. The only strikes against it would seem to be the mountainous terrain of Cuba and Jamaica, plus history--Cape Verdes-type hurricanes are quite rare in July. Dennis is only the 3rd tropical cyclone to form in the eastern Caribbean in July. Despite this history, I will not be surprised if this storm becomes a large and dangerous Cape Verdes-type hurricane later in the week.
In fact, this hurricane season has set the record for the earlist hurricane season with four named storms (records go back to about 1850). The previous record was set in 1959, when there were four named storms by July 7. Does all this activity in June and July portend a record-breaking hurricane season for 2005? Dr. Chris Landsea notes in his excellent Hurricane FAQ that "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."
Indeed, although four named storms formed by July 7 in 1959, the season turned out to be an ordinary one, with 11 named storms (which is average) and 7 hurricanes (one more than average). However, storms forming early in the season out in the area Dennis formed (south of 22 North Latitude and east of 78 West Longitude) are very often a harbinger of an active hurricane season. For example, take a look at 1933, when a record 21 named storms and 10 hurricanes formed, with four of the five June and July storms forming in this area.
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