Tropical Cyclone Report

Hurricane Juan

Juan made landfall near Halifax, Nova Scotia as a category two hurricane on the Saffir-Simpson Hurricane Scale, and will be recorded as one of the most damaging tropical cyclones in modern history for Halifax.

a. Synoptic History

The formation of Hurricane Juan was rather complex. Its origin was a large tropical wave accompanied by a broad area of low pressure that moved off the coast of Africa on 14 September and continued westward over the tropical Atlantic. On 20 September, the shower activity increased significantly but remained disorganized. By then, the wave was located about 600 n mi east of the Lesser Antilles and interacting with the circulation of a large upper-level low. This low was partially associated with the outflow of powerful Hurricane Isabel, then located well to the northwest, and the mid-oceanic upper-level trough. The wave spawned a middle-level circulation that moved northwestward away from the Lesser Antilles around the upper-low and then interacted with a frontal zone. A low-level circulation developed late on the 23^rd, but there was not enough organized convection to classify the system as a tropical depression. The disturbance had some extratropical characteristics since it appeared to be attached to the frontal zone. However, it made the transition to a tropical cyclone, when the deep convection increased near the center and the cyclone developed banding features with a distinct outflow. It is estimated that a tropical depression formed at 1200 UTC 24 September, about 300 n mi southeast of Bermuda. The cyclone reached tropical storm status by 0000 UTC September 25. The cloud pattern continued to organize and the cyclone developed an eye, becoming a hurricane by 1200 UTC 26 September.

Juan moved toward the north and then toward the northwest as the subtropical ridge to the northeast of the cyclone briefly expanded westward. The cyclone gradually intensified and reached its maximum intensity of 90 knots, with a minimum pressure of 969 mb, at 1800 UTC 27 September. Juan then turned northward again, with an increase in forward speed, and made landfall near Halifax, Nova Scotia, between Prospect and Peggy's Cove around 0300 UTC 29 September with estimated 1-min sustained winds of 85 knots and a minimum pressure of 973 mb. The cyclone weakened, but it crossed Nova Scotia as a hurricane and retained its tropical characteristics as it moved over Prince Edward Island. It became absorbed by a large extratropical low by 1800 UTC 29 September in the Gulf of St. Lawrence.

The "best track" chart of the tropical cyclone's path is given in Figure 1, with the wind and pressure histories shown in Figure 2 and Figure 3, respectively. The best track positions and intensities are listed in Table 1.

b. Meteorological Statistics

Observations in Hurricane Juan (Figure 2 and Figure 3) primarily consists of 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). Ship and buoy observations and surface reports of winds of tropical storm force or higher associated with Juan are given in Table 2 and Table 3, respectively.

A post-analysis of satellite imagery, scatterometer winds, AMSU data, ship and drifting buoy observations indicate that Juan had reached tropical storm strength by 0000 UTC 25 September. Data from a QuikSCAT pass at 0925 UTC 25 September (indicated by an X in Figure 2) suggest that the winds associated with Juan were between 40 and 45 knots. AMSU data were used to classify the cyclone as tropical since it showed a weak warm core at the mid- to upper levels of the cyclone. In addition, as the developing center passed near the drifting buoy 41537, the surface pressure dropped to 992.6 mb at 2000 UTC from 996.6 mb at 1800 UTC. This suggested that Juan had the tight inner core of a tropical cyclone. Operationally, Juan was upgraded to hurricane status based on the development of an eye feature on both visible and infrared satellite imagery, and AMSU data that suggested winds of 66 knots and a minimum pressure of 985 mb. However, because the convection was not very deep at such high latitude, the Dvorak intensity estimates did not support 65 knots at that time (Figure 2).

The center of Juan passed over a Canadian buoy (44142) between 2300 UTC 28 September and 0000 UTC 29 September, producing a wind change from the east at 54 knots to the southwest at 37 knots. The buoy pressure dropped to 974.7 mb.

The estimated intensity of 85 knots at landfall was primarily based on a report from McNab's Island, a small piece of land in Halifax Harbor. An anemometer at this location reported 2-min sustained wind of 81 knots. While the instrument is located at 10 m above the surface, the station elevation is 17 m above sea level. It is therefore possible that this measurement may not be fully representative of a surface winds. In addition, there was on an oil rig observation (not included on Table 3) in Halifax Harbor of sustained winds near 99 knot but at an elevation of 62 m. The instrument stopped recording at 99 knots. The intensity at landfall of 85 knots is in agreement with the estimates obtained by meteorologists from the Canadian Hurricane Center (CHC).

It is interesting to note that the wind field associated with Juan was not symmetric, probably because the transition to extratropical was beginning to take place. Wind reports provided by CHC indicate that wind gusts west of the track of Juan were half values of those to the right of its track. Radar observations from Halifax indicate that the eye diameter at landfall was 18 n mi.

c. Casualty and Damage Statistics

The last time that the city of Halifax was hit by the eyewall of a hurricane was 22 August, 1893. Juan will be recorded as one of the most damaging tropical cyclones in modern history for Halifax, N.S. Damage included widespread falling trees, power outages and damaged homes.

Hundred of Maritimers in Nova Scotia and Prince Edward Island lost power. There were four direct deaths (two inland and two marine) associated with Juan. In addition, four indirect deaths occurred in the aftermath. Halifax Harbor recorded an all time record water level of 4.9 feet above the normal tide levels, which resulted in extensive flooding of the Halifax and Dartmouth waterfront properties. The building where the CHC is located was also damaged.

d. Forecast and Warning Critique

The average official track errors for Juan were 38, 63, 87, 108, 61 and 129 n mi for the 12, 24, 36, 48, 72 and 96 h forecasts, respectively¹. Juan did not last long enough to verify any 120-h forecasts. These errors are much lower than the average official track errors for the 10-yr period 1993-2002² of 45, 81, 116, 150, 225 and 282 n mi, respectively. Table 4 includes a summary of track guidance during Juan.

Average official intensity errors were 8, 13,16, 20, 20 and 10 kt for the 12, 24, 36, 48, 72 and 96 h forecasts, respectively. The intensity errors were a bit higher than the average official intensity errors over the 10-yr period 1993-2002² of 6, 10, 13, 15, 19 and 21 kt, respectively.

It is rather difficult to determine accurately if a cyclone is tropical, subtropical or extratropical when characteristics of these various cyclone types are present, and Juan was no exception. The decision to classify the cyclone tropical was heavily based on AMSU data which showed a weak warm core at the mid- to upper levels of the cyclone. Advisories on the tropical depression were initiated on 25 September. Operationally, there was not enough evidence of a closed circulation and organization to start advisories on the 24^th. However, a post-analysis using scatterometer data from 0925 UTC 25 September, suggested that Juan had a well-defined closed circulation at that time. This data has led us to assume that there was enough circulation for Juan to be classified as a tropical depression on the 24^th, as indicated in the best track

Juan was forecast to reach Nova Scotia as a 65- to 70-kt hurricane. However, it did so with 85 knots. The fact that Juan maintained its tropical characteristics longer than anticipated continues to reflect the uncertainties and the limited skill in predicting the timing of the extratropical transition. Historically, most of the tropical cyclones affecting Nova Scotia are in their transition to an extratropical low. It was stated in the tropical cyclone discussions from the time of Juan's formation that the cyclone would likely retain its tropical characteristics at landfall. This was because Juan was forecast to spend little time over cool waters as it moved rapidly toward Nova Scotia .

A tropical storm warning was issued for Bermuda at 21,00 UTC 25 September and was discontinued at 1800 UTC 26 September. The CHC does not issue coastal hurricane warnings. Instead, a rain and high wind warning was issued for portions of Nova Scotia, Prince Edward Island and the marine areas.

Acknowledgments:

Most of the data and damage reports have been provided by meteorologists from the Canadian Hurricane center. A more detailed of the local effects in Nova Scotia can be found the web page of the Environment Canada Hurricane Center at: http://www.atl.ec.gc.ca/weather/hurricane/index_e.html

¹ All forecast verifications in this report include the depression stage of the cyclone. National Hurricane Center verifications presented in these reports prior to 2003 did not include the depression stage.

² Errors given for the 96 h periods are averaged over the two-year period 2001-2002.

Figure 1: Best track positions for Hurricane Juan, 24-29 September, 2003. Track after landfall was based on analyses from the Canadian Hurricane Center.

Figure 2: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Juan, 24-29 September, 2003.

Figure 3: Selected pressure observations and best track minimum central pressure curve for Hurricane Juan, 24-29 September, 2003.