Tropical Cyclone Report

Hurricane Ivan

Ivan was a classical, long-lived Cape Verde hurricane that reached Category 5 strength three times on the Saffir-Simpson Hurricane Scale (SSHS). It was also the strongest hurricane on record that far south east of the Lesser Antilles. Ivan caused considerable damage and loss of life as it passed through the Caribbean Sea.

a. Synoptic History

Ivan developed from a large tropical wave that moved off the west coast of Africa on 31 August. Although the wave was accompanied by a surface pressure system and an impressive upper-level outflow pattern, associated convection was limited and not well organized. However, by early on 1 September, convective banding began to develop around the low-level center and Dvorak satellite classifications were initiated later that day. Favorable upper-level outflow and low shear environment was conducive for the formation of vigorous deep convection to develop and persist near the center, and it is estimated that a tropical depression formed around 1800 UTC 2 September. Figure 1 depicts the "best track" of the tropical cyclone's path. The wind and pressure histories are shown in Figure 2a and Figure 3a, respectively. Table 1 is a listing of the best track positions and intensities.

Despite a relatively low latitude (9.7°N), development continued and it is estimated that the cyclone became Tropical Storm Ivan just 12 h later at 0600 UTC 3 September. Ivan continued on a generally westward motion south of 10°N latitude and steadily strengthened, becoming a hurricane at 0600 UTC 5 September centered about 1000 n mi east of Tobago in the southern Windward Islands. After reaching hurricane strength, the rate of intensification increased dramatically and Ivan underwent an 18 h period of rapid intensification (rate > 30 kt/24 h). Satellite intensity estimates suggest that the intensity increased 50 kt while the central pressure decreased 39 mb during that time and Ivan reached its first peak intensity of 115 kt at 0000 UTC 6 September. This made Ivan the southernmost major hurricane on record. However, almost as quickly as Ivan strengthened it also weakened -- as much 20 kt over the following 24 h. Conventional and microwave satellite data indicated the probable cause of the rapid weakening was due to mid-level dry air that got wrapped into the center of the hurricane and eroded the eyewall convection.

Immediately following the 24 h weakening period, Ivan began a second strengthening phase (Figure 2b) that also contained a 12 h period of rapid intensification. During that time, Ivan was under surveillance by U.S. Air Force Reserve reconnaissance aircraft as the hurricane approached the southern Windward Islands. Reports from the aircrew indicated that Ivan had strengthened to a strong category 3 (SSHS) hurricane as the center passed about 6 n mi south-southwest of Grenada. The eye diameter at that time was about 10 n mi, and the strongest winds raked the southern portion of the island.

After passing Grenada and into the southeastern Caribbean Sea, the hurricane's intensity leveled off until 1800 UTC on 8 September when another brief period of rapid intensification ensued. Reconnaissance aircraft data indicated Ivan reached its second peak intensity -- 140 kt and category 5 strength (SSHS) -- just 12 h later. This was the first of three occasions that Ivan reached the category 5 level. The previous west-northwestward motion of 14-15 kt gradually decreased while Ivan moved across the central Caribbean Sea toward Jamaica. Although a large subtropical ridge to the north remained intact, steering currents weakened and Ivan's forward speed decreased to less than 10 kt on 11 September while the hurricane made a turn to the west, keeping the center at least 20 n mi offshore the southern coast of the island. As Ivan passed south of Jamaica it weakened to category 4 strength, in part, due to an eyewall replacement or concentric eyewall cycle (Figure 4a). The combination of the westward turn and weakening kept the strongest winds offshore.

Later that day Ivan began moving west-northwestward away from Jamaica. Ivan rapidly intensified to category 5 strength a second time while it remained in a low vertical shear environment, and reached its third peak intensity at 1800 UTC 11 September. However, Ivan only maintained its maximum intensity of 145 kt and category 5 status for 6 h before it weakened back to a category 4 hurricane on 12 September. The weakening trend was short-lived and Ivan re-strengthened to category 5 for its third and final time when it was about 80 n mi west of Grand Cayman Island. Although Ivan was weakening while the center passed south of Grand Cayman on 12 September, the hurricane still brought sustained winds just below category 5 strength (Table 3) to the island. This resulted in widespread wind damage, and a storm surge that completely over swept the island except for the extreme northeastern portion.

On 13 September, Ivan approached a weakness in the subtropical ridge over the central Gulf of Mexico and turned northwestward at a slower speed of 8-10 kt. As Ivan moved over the northwestern Caribbean Sea, the combination of the impressive upper-tropospheric outflow that was being enhanced by the south-southwesterly upper-level flow ahead of an approaching trough and the very warm water in that region probably helped the hurricane maintain category 5 strength for an unusually long 30 h. Once again major land areas were spared the full force of the hurricane because the 20 n mi diameter eye and strongest winds passed through the Yucatan channel just off the extreme western tip of Cuba (Figure 4b). Hurricane force conditions were reported across portions of western Cuba, but the effects were far less than what occurred on Grenada, Jamaica, and Grand Cayman when Ivan passed those areas.

Shortly after emerging over the southern Gulf of Mexico early on 14 September, Ivan turned north-northwestward and then northward. A steady weakening trend also ensued as moderate southwesterly flow on the east side of a large mid- to upper-level trough over the central United States and northeastern Mexico gradually caused the vertical shear to increase across the hurricane. As Ivan neared the northern U.S. Gulf coast, the upper-level wind flow ahead of the trough became more westerly and strengthened to more than 30 kt, which helped to increase the shear even more and advect dry air into the inner core region. Despite the unfavorable environmental conditions, the presence of cooler shelf water just offshore and eyewall replacement cycles, Ivan weakened only slowly and made landfall as a 105 kt hurricane (category 3 on the SSHS; see Figure 2c and Figure 3b.) at approximately 0650 UTC 16 September, just west of Gulf Shores, Alabama. By this time, the eye diameter had increased to 40-50 n mi (Figure 4c), which resulted in some of the strongest winds occurring over a narrow area near the southern Alabama-western Florida panhandle border.

After Ivan moved across the barrier islands of Alabama, the hurricane turned north-northeastward across eastern Mobile Bay and weakened into a tropical storm 12 h later over central Alabama. A gradual turn to the northeast occurred shortly thereafter and Ivan became a tropical depression by 0000 UTC 17 September over northeast Alabama. A northeastward motion at 10-14 kt continued for the next 36 h before Ivan merged with a frontal system and became an extratropical low over the DelMarVa peninsula around 1800 UTC 18 September. However, even as a weak tropical depression, Ivan was a prodigious rain and tornado producer causing flash floods and tornado damage across much of the southeastern United States.

Even as an extratropical low, the remnant circulation of Ivan was identifiable in both surface and upper-air data. Over the next 3 days, the low moved south and southwestward and eventually crossed the southern Florida peninsula from the Atlantic the morning of 21 September and emerged over the southeastern Gulf of Mexico later that afternoon. As Ivan moved westward across the warm water of the Gulf, the low began to re-acquire warm core, tropical characteristics as showers and thunderstorms started developing near the well-defined low-level circulation center. During the morning of 22 September, Ivan completed a large anticyclonic loop and by 1800 UTC reconnaissance aircraft reports indicated that it had become a tropical depression again over the central Gulf of Mexico. Ivan regained tropical strength 6 h later when it was located about 120 n mi south of the mouth of the Mississippi River. Tropical Storm Ivan turned northwestward and made landfall as a tropical depression in extreme southwestern Louisiana around 0200 UTC 24 September. After landfall, Ivan quickly dissipated later that morning over the upper Texas coastal area about 20 n mi northwest of Beaumont. Including its extratropical phase, Ivan existed for 22.5 days and produced a track more than 5600 n mi long.

b. Meteorological Statistics

Observations in Ivan (Figure 2 and Figure 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the U. S. Air Force Weather Agency (AFWA), as well as flight-level and dropwindsonde observations from flights of the 53^rd Weather Reconnaissance Squadron of the U. S. Air Force Reserve Command (AFRES), and flight-level and stepped frequency microwave radiometer (SFMR) observations from the NOAA Aircraft Operations Center. Microwave satellite imagery from NOAA polar-orbiting satellites, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, and Defense Meteorological Satellite Program (DMSP) satellites were also helpful in monitoring Ivan. In addition, National Weather Service Doppler radars (Slidell, LA, Mobile, AL, and Elgin AFB, FL) were extremely useful for tracking this tropical cyclone. An example is seen in Figure 4, a reflectivity image of Ivan shortly after the time of landfall on 16 September from the Mobile WSR-88D Doppler radar, which shows the large eye of the hurricane inland over extreme southern Alabama.

A total of 112 reconnaissance center investigations were made in Ivan - 95 by the U.S. Air Force Reserve and 17 by the NOAA Hurricane Hunters. In addition, the NOAA Gulfstream-IV jet aircraft conducted 12 synoptic surveillance flights around the periphery of the hurricane. The maximum flight-level (700 mb) wind observed was 161 kt at 1917 UTC 11 September, when Ivan was located about 45 n mi west-southwest of the western tip of Jamaica. However, during Ivan's traversal across the Caribbean Sea, there were 12 additional flight-level wind reports of 150 kt or greater. The lowest aircraft measured pressure was 910 mb at 0005 UTC 12 September, less than 5 h after the maximum flight-level wind was observed, and also at 2053 UTC 13 September, which was about 2 h after flight-level winds of 157 kt were measured on two separate flight legs. Several research flights were made by NOAA aircraft when Ivan was moving over the Gulf of Mexico. The maximum SFMR surface wind observed was 99 kt at 0135 UTC 16 September about 58 n mi south of the Alabama coast. In the Caribbean Sea area, the maximum observed wind over land was sustained 130 kt with a gust to 149 kt on Grand Cayman Island at 1345 UTC 12 September. A 10-min average wind of 116 kt was reported at Pedro Bank, which is about 50 n mi southwest of Kingston. This was also the upper limit of reporting range of the wind observing equipment. Doppler radar velocity data indicated wind speeds as high as 97 kt may have affected much of Jamaica, especially over the higher elevations. In the United States, the strongest winds measured were an unofficial report from a storm chaser near Gulf Shores, Alabama of sustained 77 kt with a gust to 99 kt at 0602 UTC 16 September. Also, an unofficial wind gust of 126 kt at approximately 0600 UTC 16 September was observed by the sailboat Odalisque anchored in Wolf Bay north of Orange Beach, Alabama. The highest official wind report was 76 kt sustained with a gust to 93 kt at the Pensacola Naval Air Station, Florida at 0629 UTC 16 September.

The lowest pressures observed during Ivan's first U.S. landfall were unofficial reports 943.1 mb and 947.9 mb, which came from storm chasers based in Fairhope, Alabama. In addition, an automated weather observing station (AWOS) on the oil drilling platform Ram Powell-VJ956, located about 70 n mi south of Mobile Bay, Alabama (Table 3) reported a sustained wind of 102 kt with a gust to 135 kt at 2256 UTC 15 September at an elevation of 400 ft ASL. The instrument failed immediately after this report was obtained and remained inoperable for the next 4 days. Aircraft reconnaissance reports around that time suggest that the oil rig was located north-northeast of Ivan's center and just outside the radius of maximum winds.

Although Ivan was weakening as it made its first U.S. landfall, it is estimated to have been a category 3 hurricane when it reached the Alabama coast. As Ivan neared the U.S. Gulf coast on 15 and 16 September, the hurricane came under the surveillance of National Weather Service (NWS) WSR-88D Doppler radars located in Slidell, LA, Mobile, AL, and Eglin AFB, FL There was a robust and persistent velocity maximum located within vigorous convection in the northeastern quadrant of the outermost concentric eyewall as Ivan was coming ashore. For several hours prior to landfall, the velocities were actually higher in this area than in the vicinity of the inner eyewall. Within the outer eyewall existed several 1-2 n mi² patches of 120-122 kt inbound Doppler velocities (some individual gates contained 123.4 kt velocities) at around 6,000 ft ASL. Using 122 kt as being representative of a smoothed peak and applying a reduction factor of 0.85 (standard reconnaissance flight-level reduction for 6000 ft) yields a surface estimate of 104 kt. In addition to the Doppler radar velocity data, a 700 mb flight-level wind of 120-kt was observed just south of Gulf Shores, AL at 0724 UTC 16 September (Figure 2c) in the same general area where the aforementioned maximum Doppler radar velocities were observed. The 120-kt flight-level wind converts to approximately a 108-kt surface wind using the standard 0.90 reduction factor from the 700 mb-level. A blend of those two equivalent surface wind values yields an intensity of 105 kt Ivan's first U.S. landfall. This intensity estimate is also consistent with the 99-kt SFMR surface wind data that was collected by a NOAA WP-3 aircraft more than 6 h before landfall. In addition, assuming a typical outward slope to the eyewall, the narrow band of strongest winds at landfall likely occurred over Perdido Key and Perdido Bay, which would have been to the west of the Pensacola Naval Air Station and to the east of the Florida Coastal Monitoring Program portable wind tower at Gulf Shores, Alabama.

Ship reports of winds of tropical storm force associated with Ivan are given in Table 2, and selected surface observations from land stations and data buoys are given in Table 3, Table 4, and Table 5. With the exception of a couple of ships that had sought shelter in the harbors around Grenada, the majority of ships remained clear of Ivan's strong winds.

Heavy rainfall exceeding 10 inches occurred on several of the Caribbean Islands (Table 3 and Table 5) and caused extensive freshwater flooding and/or mud slides. Some peak rainfall totals are 16.20 in from Tobago, 13.33 in from western Cuba, and 12.14 in from Grand Cayman. Across Jamaica, several locations received more than 25 in (635 mm) of rainfall. A few of the largest rainfall totals were 28.37 in (720.8 mm) at Ritchies, 27.92 in (709.4 mm) at Mavis Bank, and 26.83 in (681.5 mm) at both Craighead and Worthy Park. The Meteorological Service of Jamaica also "noted that rainfall data representative of a number of stations in southern parishes were lost due to damage done to rain gages by Hurricane Ivan." In the United States, rainfall totals generally ranged from 3-7 in along a large swath from Alabama and the Florida panhandle northeastward across the eastern Tennessee Valley and into the New England area (Figure 6) In fact, when Ivan was an extratropical low pressure system, it produced rainfall totals in excess of 7 in as far north as New Hampshire and as far south as the Florida east coast. Even as a weakening tropical depression, Ivan produced rainfall amounts exceeding 7 in across eastern Texas. However, there were two isolated extreme rainfall reports exceeding 15 in -- 15.75 in at television station WEAR-TV3 in Pensacola, Florida and 17.00 in at Cruso, North Carolina. Widespread flooding resulted from Ivan's rains, which fell on already saturated ground caused by Tropical Storm Bonnie and Hurricane Frances that traversed much of the same area in August and early September.

An outbreak of 117 tornadoes -- with the bulk of the tornadoes on 17 September -- developed over a 3 day period in the United States, including 37 in Virginia, 25 in Georgia, 18 in Florida, 9 in Pennsylvania, 8 in Alabama, 7 in South Carolina, 6 in Maryland, 4 in North Carolina, and 3 in West Virginia. There were 26 tornadoes reported on 15 September, 32 tornadoes on 16 September, 57 tornadoes on 17 September, and 2 tornadoes (in Maryland) on 18 September. At least 8 people were killed and 17 injured by the tornadoes. On 15 September, some of the more significant tornado events occurred -- an F2 tornado occurred near Panama City Beach (Bay Co.), FL resulting in 1 death and 7 injuries; a second F2 tornado occurred near Blountstown (Calhoun Co.), FL resulting in 4 deaths and 1 injury; a third tornado (intensity undetermined) killed 2 people in Panama City, FL a little more than 1 h after the F2 tornado had struck the area.

Storm surge of 10-15 ft occurred along the coasts from Destin in the Florida panhandle westward to Mobile Bay/Baldwin County, Alabama. Storm surge values of 6-9 ft were observed from Destin eastward to St. Marks in the Florida Big Bend region. Lesser values of storm surge continued east and southward along the Florida west coast with 3.5 ft reported in Hillsborough Bay/Tampa Bay. There was also a possible record observed wave height of 52.5 ft reported by the NOAA Buoy 42040 located in the north central Gulf of Mexico south of Alabama. In addition, severe storm surge flooding of 8-10 ft with 20-30 ft waves caused more than 5-8 ft of water to cover Grand Cayman Island at times. This resulted in the airport and numerous homes being completely inundated by sea water.

c. Casualty and Damage Statistics

The forces of Ivan were directly responsible for 92 deaths - 39 in Grenada, 25 in United States, 17 in Jamaica, 4 in Dominican Republic, 3 in Venezuela, 2 in Cayman Islands, and 1 each in Tobago and Barbados. Concerning the deaths in the United States, 14 occurred in Florida, 8 in North Carolina, 2 in Georgia, and 1 in Mississippi. The breakdown of U.S. deaths by cause is as follows: tornado (7), storm surge (5), fresh water floods (4), mud slides (4), wind (3), and surf (2). Ivan was also indirectly responsible for 32 deaths in the United States.

Ivan caused extensive damage to coastal and inland areas of the United States. Portions of the Interstate 10 bridge system across Pensacola Bay, Florida were severely damaged in several locations as a result of severe wave action on top of the 10-15 ft storm surge. As much as a quarter-mile of the bridge collapsed into the bay. The U.S Highway 90 Causeway across the northern part of the bay was also heavily damaged. To the south of Pensacola, Florida, Perdido Key bore the brunt of Ivan's fury and was essentially leveled. Along the Alabama coast, high surf and wind caused extensive damage to Innerarity Point and Orange Beach. In the Alabama and Florida panhandle areas, widespread over wash occurred along much of the coastal highway system. In addition, extensive beach erosion caused severe damage to or the destruction of numerous beachfront homes, as well as apartment and condominium buildings. Some buildings collapsed due to scouring of the sand from underneath the foundations caused by the inundating wave action. Thousands of homes the three-county coastal area of Baldwin, Escambia, and Santa Rosa were damaged or destroyed. Cleanup efforts alone in Escambia County resulted in debris piles that were more than three-quarters of a mile long and 70 feet high. In all, Ivan was the most destructive hurricane to affect this area in more than 100 years. Strong winds also spread well inland damaging homes, and downing tress and power lines. At one point, more than 1.8 million people were without power in nine states.

In addition to the damaged homes and businesses, Ivan also destroyed millions of acres of woodlands and forests. The Alabama Forestry Commission found damaged timber valued at about $610 million on 2.7 million acres. These figures include

• Pine pulpwood: 7.5 million cubic feet
• Hardwood pulpwood: 2.6 million cubic feet
• Pine sawtimber: 351.5 million board feet
• Hardwood sawtimber: 493 million board feet.

In the 200,000-acre Blackwater Forest, just east of Pensacola in the western Florida panhandle, more than 1.5 million board feet of timber were downed across 185,000 acres.

Ivan's effects were not just limited to coastal and inland areas. Offshore oil industry operations in the Gulf of Mexico were severely disrupted, and several oil drilling platforms and pipelines sustained varying degrees of damage. The normal daily flow of 475,000 barrels of oil and 1.8 billion cubic feet of natural gas, plus refining operations, were disrupted for more than 4 weeks. A total of 12 large pipelines and 6 drilling platforms sustained major damage; another 7 platforms were completely destroyed.

A total of 686,700 claims were filed and the American Insurance Services Group estimates (14 December 2004 re-survey) that insured losses in the United States from Hurricane Ivan totaled $7.11 billion, of which more than $4 billion occurred in Florida alone. Using a two-to-one ratio of insured damages yields an estimated U.S. loss of approximately $14.2 billion. In addition to the insured losses that occurred, the U.S. Naval Air Station at Pensacola, Florida sustained damage losses of $800-$900 million.

In the Caribbean region, extensive damage occurred to homes, buildings and other structures. The following are brief synopses of the reports received from some of the Caribbean islands:

Barbados

More than 176 homes completely destroyed; many homes lost their roofs; most coastal roads severely damaged due to erosion caused by the storm surge and wave action.

Cayman

95 percent of the homes and other buildings (which generally follow South Florida's building codes) were damaged or destroyed.

Cuba

Roofs were torn off homes in extreme western Pinar del Rio Province; flooding damaged houses, and fishing and farm installations; mud slides cut off at least two towns.

Grenada

At least 80 percent of the 100,000 residents were without power; more than 14,000 homes were damaged or destroyed; 80 percent of the nutmeg trees were destroyed; a 17^th century prison was also damaged allowing many of the inmates to briefly escape during the height of the storm; Ivan was the worst hurricane to strike the island since Hurricane Janet in 1955.

Jamaica

At least 47,000 homes were damaged, of which 5,600 were completely destroyed; most of the islands utilities were damaged.

St. Vincent/Grenadines

50 homes severely damaged with 2 homes washed away into the sea; more than two-thirds of residents lost power.

Tobago

At least 1 home collapsed and fell into the ocean; at least 45 homes lost their roofs; numerous trees and utility were blown down; 20 villages suffered various forms of damage

In the Caribbean Sea region, the Caribbean Development Bank (CDB) estimates the damage at more than US$3 billion -- US$1.85 billion in the Cayman Islands, US$815 million in Grenada, US$360 million in Jamaica, US$40 million in St. Vincent and the Grenadines, and US$2.6 million in St Lucia. No damage estimates were available from any of the other Windward Islands countries, Venezuela, or Cuba.

d. Forecast and Warning Critique

Average official track errors (with the number of cases in parentheses) for Ivan were 24 (63), 47 (61), 79 (59), 108 (56), 161 (52), 222 (48), and 289 (44) n mi for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. In comparison, the longer-term average official track errors for the 10-yr period 1994-2003^[1] are 44, 78, 112, 146, 217, 248, and 319 n mi. Table 6 contains the average errors from various numerical track forecast models for Ivan. The average NHC official track forecast (OFCL) errors for Ivan were better than the 10-yr average throughout the 120 h forecast cycle, especially through 72 h. However, most of the various numerical track forecast models, like the UKMET and FSU Superensemble (FSSE) models outperformed the NHC official track forecast at most times. On average, the FSSE model significantly outperformed the NHC official forecast at all times. Average official intensity errors were 9, 12, 13, 12, 15, 24 and 36 kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1994-2003 are 6, 10, 12, 15, 19, 20, and 21 kt, respectively. These intensity errors were greater than average at 96 and 120 h due to rapid intensification and greater than forecast intensities that occurred over the Caribbean Sea. Synoptic-scale analyses produced by the NOAA Global Forecast System (GFS) indicate that Ivan essentially remained underneath a 200 mb ridge axis as the hurricane traversed the Caribbean Sea. This resulted in implied relatively low 850-200 mb vertical wind shear values ( < 10 kt in many times periods) over the inner core region and also provided favorable upper-level outflow channels to the north and south. However, the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model failed to capture both the early rapid intensification period and the lengthy period of category 4 and 5 strength. This may be due to the way the SHIPS model assesses the vertical shear across a tropical cyclone. During the period 7-14 September when significant intensification occurred, the SHIPS model assessed the vertical shear on numerous occasions to be 15-20 kt from a westerly direction. Typically when alleged westerly shear of this magnitude is present, little or no strengthening occurs and, more often, weakening transpires. The westerly vertical shear calculated by the SHIPS model may have been due, in part, to its inability to separate the strong upper-level outflow from the environmental flow in which the cyclone was embedded.

Official track forecasts had, in general, a persistent right-of-track bias for the first 11 days of Ivan's existence as a tropical cyclone (Figure 5a). The official track forecasts relied heavily on the global model forecasts, which prematurely eroded the large and strong subtropical ridge to the north of Ivan that extended well westward across the Bahamas, Florida, and into the Gulf of Mexico. In fact, several of the GFS model forecast cycles consistently eroded the ridge across Bahamas and took Ivan well to the east of Florida, even as the hurricane was approaching Jamaica. The westward jog that Ivan made on 11 September appears to be, at least in part, the result of a mid- to upper-level cold low to the north of Hispaniola that moved slowly southwestward rather than weakening and lifting out to the northeast as some of the models had been forecasting. Despite the early right bias, once Ivan moved into the northwestern Caribbean Sea, the track forecasts gradually narrowed down the likely landfall region of the western Florida panhandle and Alabama coasts (Figure 5b). Table 7 lists all of the watches and warnings issued for Ivan.

A hurricane watch was issued for the central U.S. Gulf coast more than 51 h prior to landfall on the Alabama coast. A hurricane warning was issued for the same area less than 42 h prior to landfall. Over the 72 h period leading up to the first U.S. landfall, there was a spread of only 95 n mi between the westernmost and easternmost forecast tracks. In fact, more than 75% of those forecasts targeted the Alabama coast as the most likely area where landfall was expected to occur. The result of these forecasts was that Ivan made landfall well within the area covered by the hurricane watch and warning.

Acknowledgments

NWS/WFOs Houston/Galveston, Huntsville, Jacksonville, Key West, Lake Charles, Mobile, New Orleans (Slidell), Tallahassee, and Tampa Bay, and the NOAA Hydrometeorological Prediction Center and the NOAA Southeast River Forecast Center contributed many of the observations contained in this report. Amateur Radio (HAM) operators throughout the Caribbean region and those working as part of the National Hurricane Center's WX4NHC Hurricane WatchNet team ( http://www.fiu.edu/orgs/w4ehw/) were indispensable in providing critical reports as Ivan moved through the Windward Islands and across the Caribbean Sea.

^[1]Errors given for the 96 and 120 h periods are averages over the three-year period 2001-3.

Figure 1: Best track positions for Hurricane Ivan, 2-24 September 2004.

Figure 2a: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Ivan, 2-24 September 2004. Aircraft observations have been adjusted for elevation using 90%, 80%, and 80% reduction factors for observations from 700 mb, 850 mb, and 1500 ft, respectively.

Figure 2b: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Ivan during the peak intensity period of 9-16 September 2004.

Figure 2c: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Ivan approximately 24h prior to and 18 h after landfall (15-17 September 2004) along the Alabama coast. The highest surface winds occurred along the extreme western Florida panhandle coastal areas, well east of where the center actually made landfall along the Alabama coast.

Figure 3a: Pressure observations and minimum central pressure curve for Hurricane Ivan, 2-24 September 2004.

Figure 3b: Pressure observations and minimum central pressure curve for Hurricane Ivan during its period of greatest intensity (9-16 September 2004).

Figure 4a: Radar reflectivity image from Kingston, Jamaica at 1444 UTC 10 September 2004 as Ivan was approaching the island from the southeast. Ivan had weakened from a category 5 hurricane down to category 4 hurricane with sustained winds of 125 kt at this time. Note the two concentric eyewalls that likely were the cause of the short term weakening (image courtesy of the Jamaica Meteorological Service).

Figure 4b: Radar reflectivity image from Cancun, Mexico at 2342 UTC 13 September 2004. Ivan was a category 5 hurricane with sustained winds of 140 kt and a pressure of 914 mb at this time (image courtesy of the National Meteorological Service of Mexico).

Figure 4c: Reflectivity image of Hurricane Ivan from the Mobile, AL National Weather Service Forecast Office WSR-88D Doppler radar at 0702 UTC 16 September 2004 -- less than 15 min after the time of landfall along the Alabama coast. The center of the broad eye of the hurricane was inland over extreme southern Alabama at this time. An Air Force Reserve reconnaissance aircraft reported flight-level winds of 120 just offshore in the strong convective band (red 50 dBZ areas) southwest of Pensacola, Florida at about 20 min after the time of this image. Peak Doppler radar velocities ranged from 120-123 kt at 6,000 ft ASL as Ivan moved onshore.

Figure 5a: NHC Official forecast tracks (OFCL) for Hurricane Ivan during the period 1800 UTC 02 through 0600 UTC16 September 2004 (1^stU.S.landfall). Note the persistent right-of-track bias from the outset as a result of most of the global models prematurely eroding the subtropical ridge to the north of the hurricane.

Figure 5b: NHC Official forecast tracks (OFCL) for Hurricane Ivan during the period 0600 UTC 13 September to 0000 UTC 16 September 2004. Note the small spread in the forecast tracks (from 72 h through 6 h prior to landfall), which targeted the Alabama and extreme western Florida panhandle coastal areas as the most likely region where landfall would occur.

Figure 6: United States rainfall totals for Hurricane Ivan (image courtesy of NOAA Hydrometeorological Prediction Center).