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Preliminary Report
Hurricane Erika
03 - 15 September 1997

Miles B. Lawrence
National Hurricane Center
24 October 1997

Subtropical Storm
Tropical Storm Ana
Hurricane Bill
Tropical Storm Claudette
Hurricane Danny
Tropical Depression Five
Hurricane Erika
Tropical Storm Fabian
Tropical Storm Grace

[1997 Atlantic Hurricane Season]

a. Synoptic History

Erika became a category three hurricane on the Saffir/Simpson Hurricane Scale, was the only named tropical cyclone of 1997 to form from a tropical wave at low latitudes, and just missed the islands of the northeastern Caribbean Sea.

Erika was first tracked as a tropical wave and large area of disturbed weather moving westward from Africa to the eastern tropical Atlantic Ocean on 31 August. The system immediately showed evidence of a large-scale low-level cyclonic turning. But it was not until 3 September, when located about 1000 nautical miles east of the Lesser Antilles, that a low-level center was defined well enough for it to be upgraded to a tropical depression. The best track begins at this time as shown in Fig. 1 (52K GIF) and as listed in Table 1.

The depression quickly strengthened to tropical storm Erika on the 3rd and to a hurricane on the 4th as it moved mostly west-northwestward at 15 knots or so under the steering control of a well-established subtropical high pressure ridge. There was a hint of an eye as infrared satellite imagery showed a warm spot embedded in the deep convection over the center early on the 4th, but visible satellite imagery later showed a partially exposed low level center. The strengthening of Erika to a hurricane, based on drifting buoy data east of the Lesser Antilles, occurred under what appears to be an unfavorable shearing situation. However, deep convection soon reappeared over the center and strengthening continued, while Erika moved toward the west-northwest.

On the 5th through the 8th, the forward motion gradually decreased as the center of the hurricane came within about 75 nautical miles to the northeast of the northeastern-most Lesser Antilles...just far enough away for hurricane conditions to miss these islands. By the 8th, Erika had turned toward the north with a movement of only five knots as an amplifying trough over the western north Atlantic eroded the subtropical ridge and weakened the nearby steering currents.

Erika reached its peak intensity of 110 knots at 1800 UTC on the 8th and retained this wind speed for a period of about 24 hours, while it was located 300 nautical miles north of the Caribbean islands and started to accelerate northward. Reconnaissance aircraft and satellite imagery indicated an eye diameter of about 30 nautical miles during this time and the hurricane's radius of tropical storm force wind speeds expanded to 250 nautical miles.

The hurricane passed about 300 nautical miles east of Bermuda on the 10th and became embedded in westerly steering currents which caused a turn toward the east-northeast on the 11th and 12th. By this time, weakening had commenced due to a combination of cool sea surface temperatures and westerly winds aloft. Winds dropped below hurricane force on the 12th. However, Erika periodically retained deep convection near its center for another four days along with wind speeds between 45 and 60 knots while it moved mostly eastward across the north Atlantic. The center passed very near the western-most Azores on the 15th and tropical storm conditions were experienced in these islands. Erika then lost most of its deep convection and became extratropical by the 16th. It continued moving northeastward for several more days, followed by dissipation on the 20th while located about 200 nautical miles southwest of Ireland.

b. Meteorological Statistics

Figures 2 (22K GIF) and 3 (25K GIF) show curves of minimum sea-level pressure and maximum one-minute surface wind speed, respectively, as a function of time. Satellite data plotted in these figures are based on the Dvorak satellite intensity estimating technique as applied at the Tropical Analysis and Forecast Branch (TAFB), the Synoptic Analysis Branch (SAB) and the U.S. Air Force Global Weather Center (AFGWC).

Ship reports of wind speeds of 34 knots or higher caused by the hurricane are listed in Table 2. The large number of such reports in northern latitudes is the result of Erika's path through the north Atlantic shipping lanes.

The NOAA Gulfstream high-altitude jet flew missions which resulted in data available for the 0000 UTC NCEP model runs on the 4th and 5th. This was when Erika was threatening the Caribbean islands and several days in advance of the recurvature across the north Atlantic. This data set provides an opportunity to evaluate the impact of synoptic-scale high-altitude dropsonde missions.

A NOAA drifting data buoy reported a 60-knot wind speed at 1600 UTC on the 4th, when Erika was located some 500 nautical miles east of the Lesser Antilles. The best track takes Erika to a hurricane at 1800 UTC based on this report, although there is considerable uncertainty about the accuracy of drifting buoy wind measurements as well as the method used to adjust the wind speed to the 10 meter level.

There were no reports of tropical storm force or higher sustained winds from the islands of the northeastern Caribbean as Erika passed nearby. The highest report received was 32 knots sustained wind speed with gusts to 41 knots from St. Thomas in the U.S. Virgin Islands on the 7th, when Erika was centered 125 nautical miles north-northeast of this location. There were, undoubtedly, stronger winds over the higher terrain of the islands from the Virgin Islands east and southward through Antigua and Montserrat. The largest rainfall total reported from the islands is 3.28 inches from St. Thomas.

NOAA research aircraft dropped GPS dropsondes into the eye wall on the 7th and 8th, as Erika was strengthening to its maximum intensity. While maximum 700-millibar flight level winds were near 110 knots late on the 8th, the vertical wind profile obtained near the eye wall showed that wind speeds between 150 and 1500 meters reached nearly 50 percent higher. The wind speed from this dropsonde nearest to the surface (approx. 15 meters) was 117 knots and the best track surface wind speed of 110 knots is based on this data.

The highest sustained surface wind report seen from the Azores was 26 knots with a gust to 39 knots at Lajes Air Base at 1900 UTC on the 15th as Erika's center was passing 180 nautical miles to the northwest. A report from Flores at 2300 UTC on the 15th gave a gust to 76 knots. A report from Lajes showed a gust to 91 knots from a 200-foot tower. A storm rainfall total of 2.35 inches was also reported from Flores.

c. Casualty and Damage Statistics

The only effects to Puerto Rico were from the large waves and swells generated by the hurricane. Two surfers died in the northern and eastern waters due to the high wave action. Most of the islands of the northeastern Caribbean suffered minor damage from wave action and there was likely minor wind damage at higher elevations. The general mood as expressed in the media was one of relief that a dangerous hurricane had turned north and missed the islands.

The passage of the hurricane caused the lower-tropospheric winds to blow from the southwest and advect a cloud of falling ash over Antigua from the active volcano in Montserrat.

d. Forecast and Warning Critique

There were 49 official forecasts issued while Erika was a tropical storm or hurricane. The average track errors were 12, 46, 78, 99, 121, and 191 nautical miles at 0, 12, 24, 36, 48, and 72 hours. These numbers are small compared to the previous official ten-year-average errors. The interpolated GFDL model errors were approximately 20 percent smaller than the official errors at 48 and 72 hours for about 30 simultaneous forecast cases. The official track forecasts also had a left bias for the few days when Erika was threatening the islands of the northeastern Caribbean Sea, which was prior to the recurvature toward the north.

The official wind speed forecasts had a negative bias just before Erika began strengthening toward its 110-knot maximum winds. Negative errors of up to 45 knots for the 72-hour forecast issued early on the 5th were the result of strengthening occurring under what appeared to be a strong vertical wind shear environment.

A list of the various watches and warnings issued for this hurricane is given in Table 3. Hurricane warnings were issued for a number of the island countries of the northeastern Caribbean Sea. Although hurricane conditions did not occur in the warning area, the storm passed sufficiently close to the islands to justify the warnings. Although tropical storm warnings were not issued for the Azores, National Hurricane Center advisories contained the equivalent statement that tropical storm conditions were expected to occur there.

Table 1. Best track, Hurricane Erika, 3 - 15 September 1997.
Position Pressure
Wind Speed
Lat. (°N)Lon. (°W)
03/060010.944.1100630 tropical depression
180012.347.1100435 tropical storm
180015.253.799965 hurricane
12/000037.649.999060 tropical storm
16/000042.228.298550 extratropical
20/0000     dissipated
09/060025.261.4946110 minimum pressure

Table 2. Ship reports of 34 knots or higher sustained winds.
KRPPNobel Star04/090015.950.8090/49 1009.5
KMJLItb Groton07/150021.860.3130/35 1008.8
KMJLItb Groton08/000020.659.7 020/86?1009.2
LADR4Star Gran08/000023.865.0050/39 1006.5
WCHFSealand Consumer08/030019.068.0 350/71?1011.7
C6QKBarrington Island10/090033.659.9 080/381001.0
C6QKBarrington Island10/120033.561.2 080/381000.5
C6QKBarrington Island10/150033.262.5 040/381004.0
9HOP3Sarajevo Express11/090037.158.8 020/451009.0
9HOP3Sarajevo Express11/150036.458.8 020/451010.0
9HOP3Sarajevo Express11/180035.758.0 320/351012.0
V7AZ5?11/180035.848.1160/42 1006.1
9HOP3Sarajevo Express11/210035.757.5360/401011.3
C6JY9Eastern Bridge14/000032.338.9 240/371007.3
ship-----14/120033.037.3260/60 1000.6
PGBOMusic14/180041.845.8360/36 1012.3
ship-----15/000033.440.0280/60 1011.1
DDSKSea Progress15/000037.428.6 140/371011.2
DDSKSea Progress15/060036.530.4 210/411005.0
DDSKSea Progress15/120035.931.4 240/441007.3
DDSKSea Progress15/150036.032.1 250/371007.5
C6LU4Hood Island15/180034.527.8 200/401013.0
4XGTZim Italia15/180037.028.6 240/451007.5
DDSKSea Progress16/000036.235.3 260/351012.0
FNRSDouce France16/060039.620.7 160/381009.7
ship-----16/060041.622.1170/51 1002.0
9VPPFrankfurt Express16/120045.026.5 010/45-----
PCDEAdmiralengracht17/000047.622.9 010/581000.4
LAHE2Star Evvivia17/120046.326.8 030/401013.0
PFEIJo Selje18/000048.720.7010/52 1004.0
PFEIJo Selje18/030048.419.8360/49 1000.9

Table 3.
Watch and warning summary, Hurricane Erika, September 1997.
04/2100 tropical storm watch issued Antigua, Montserrat, Barbuda, Nevis, St. Kitts, and Anguilla
tropical storm warning issuedDutch St. Maarten
05/0300tropical storm watch issued Guadeloupe, St. Martin, and St. Barthelemy
05/0900 tropical storm warning issued Antigua, Montserrat, Barbuda, Nevis, St. Kitts, Anguilla, and Dominica
tropical storm watch issued U.S. and British Virgin Islands
05/1200tropical storm warning issued Guadeloupe, St. Martin, and St. Barthelemy
05/1500 hurricane warning issued Antigua, Montserrat, Barbuda, Nevis, St. Kitts, Anguilla, and Dominica; St. Martin and St. Barthelemy; Dutch St. Maarten
hurricane watch issued U.S. and British Virgin Islands and Puerto Rico
06/1200discontinue tropical storm warning Guadeloupe and Dominica
06/1800discontinue hurricane warning Barbuda, Antigua, Nevis, St. Kitts, Montserrat, and Dominica
06/2100discontinue hurricane warning St. Barthelemy, St. Martin, Dutch St. Maarten, and Anguilla
07/2100discontinue hurricane warning U.S. and British Virgin Islands and Puerto Rico

Brian Maher
Jack Beven

Last updated December 26, 1998