2007 PACIFIC HURRICANE SEASON

The '2007 Pacific hurricane season' is an ongoing event in the annual cycle of tropical cyclone formation. It officially started on May 15, 2007 in the eastern Pacific, designated as the area east of 140°W; on June 1 2007 in the central Pacific, which is between the International Date Line and 140°W; and will last until November 30, 2007. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin.
The season began slowly; through the end of July, the seasonal ACE was the third lowest since the geostationary satellite era began in 1966.^[1] The inactivity continued through the next month, which was the third quietest August in terms of ACE since reliable records began in the basin in 1971.^[2] Tropical Storm Barbara in June caused $55 million (2007 USD) in crop damage in southeastern Mexico from heavy precipitation. In August, Hurricane Flossie formed in the Eastern Pacific and crossed into the Central Pacific, threatening Hawaii but causing little damage. In early September, Tropical Storm Henriette dropped heavy rainfall in southwest Mexico, which caused six fatalities.
__TOC__

Seasonal forecasts

'Predictions of tropical activity in the 2007 season
for the Eastern North Pacific'
'Source'	'Date'	'Named storms'	'Hurricanes'	'Major hurricanes'
NOAA	''Average''^[3]	15.3	8.8	4.2
NOAA	22 May 2007	12–16	6–9	2–4
	'Actual activity'	8	3	1

On May 22, 2007, NOAA released their forecast for the 2007 Eastern Pacific and Central Pacific hurricane seasons. They predicted a below-normal level of activity in the Eastern Pacific, with 12 to 16 named storms, of which 6 to 9 were expected to become hurricanes, and 2 to 4 expected to become major hurricanes.^[4]
The Central Pacific basin was also expected to be below average, with only two to three tropical cyclones expected to form or cross into the area.^[5]

Storms

Tropical Storm Alvin

A nearly-stationary low pressure area developed about 550 miles (885 km) south-southeast of Manzanillo, Mexico on May 24.^[6] Upper-level winds favored development, and the system slowly became better organized.^[7] By early on May 26, the system had developed a well-defined circulation, though associated convection had become limited.^[8] Later that day convection increased significantly over the center, and early on May 27 Tropical Depression One-E formed 345 mi (555 km) south of the tip of Baja California.^[9] Located to the east of a ridge and to the west of a trough, the depression tracked slowly westward through an area of weak steering flow.^[10]
Due to unfavorable thermodynamics of the environment, the depression failed to immediately strengthen; the convection weakened, leaving the center located well to the northeast of the poorly-organized convective areas.^[11] Inflow from the south was cut off by another area of disturbed weather to its southeast, and by late on May 27 one forecaster indicated there was inadequate convection to qualify the system as a tropical depression, although advisories continued since it was expected to strengthen again.^[12] Convection again re-developed early on May 28,^[13] and by later in the day remained vigorous but limited to the southwestern quadrant of the circulation.^[14] It consolidated further and strengthened into a tropical storm early on May 29.^[15] By later in the day, the convection again diminished, and the center of Alvin became difficult to locate on satellite imagery.^[16] Alvin was thus downgraded a tropical depression after becoming less organised on May 30.^[17] On May 31, Alvin lost all deep convection.^[18] Tropical Depression Alvin degenerated into a remnant low on June 1.

★ The NHC's Archive on Tropical Storm Alvin.

Tropical Storm Barbara

On May 27, an area of disorganized convection extended southwestward from the Gulf of Tehuantepec.^[19] On May 28, a small low pressure area developed within the system,^[20] and it gradually became better organized as it drifted northward. Banding features developed in the eastern semicircle as the circulation became better defined, and late on May 29 the National Hurricane Center classified the system as Tropical Depression Two-E while it was located about 235 miles (380 km) southeast of Acapulco, Mexico. Upon becoming a tropical cyclone, the depression was stationary in an area with warm sea surface temperatures, very light wind shear, and favorable upper-level conditions.^[21]
It became more organised on satellite imagery on May 30, and was upgraded to a tropical storm, marking only the third time that there had been two named storms in May, after 1956 and 1984.^[22] It tracked slowly southeastward for the first few days, before losing much of its organisation overnight on May 31, leading to a forecast that Barbara could dissipate later that day.^[23] It managed to re-consolidate, however, and regained tropical storm intensity on June 1, when tropical storm watches were put into place. Barbara made landfall near the Mexico-Guatemala border on June 2. Heavy rainfall from the storm caused about $55 million (2007 USD) in crop damage in southeastern Mexico.^[24]

★ The NHC's Archive on Tropical Storm Barbara.

Tropical Depression Three-E

On the evening of June 9, the National Hurricane Center first mentioned the existence of a large, disorganized area of low pressure, which was located a few hundred miles southwest of Acapulco, with limited shower activity.^[25] The associated thunderstorms gained organization overnight, and on June 10 the NHC first mentioned the possibility of some slow development of the system.^[26] Environmental conditions were favorable for tropical cyclone formation, but the system changed little in organization.^[27] The disturbance finally consolidated and became a tropical depression, the third of the season, on June 11, about 465 miles (745 km) south-southwest of Manzanillo, Mexico.^[28] However, the depression soon entered an environment of stable air and cooler sea surface temperatures and gradually weakened over the next two days. The NHC issued its last advisory early on June 13 after the system lost most of its convection.

★ The NHC's Archive on Tropical Depression 3E.

Tropical Depression Four-E

On July 9, an area of convection developed about 725 miles (1170 km) south of Manzanillo, Mexico; conditions favored slow development,^[29] and it slowly became better organized as it tracked steadily westward.^[30] A well-defined low pressure area developed within the system, and at 2100 UTC on July 9 the National Hurricane Center classified it as Tropical Depression Four-E after deep convection was maintained near its low-level circulation. Upon becoming a tropical cyclone, the depression was poorly organized,^[31] and by early on July 10 the convection greatly diminished near the ill-defined center of circulation.^[32] Later that day, deep convection redeveloped despite detrimental atmospheric and oceanic conditions,^[33] though convection again deteriorated later while the winds decreased.^[34] After continued weakening the National Hurricane Center issued the final advisory on the system early on July 11.^[35]

★ The NHC's Archive on Tropical Depression 4E.

Tropical Depression Five-E

Early on July 11, just as Tropical Depression Four-E had degenerated into a remnant low, an area of disturbed weather formed around 350 miles (560 km) south of Acapulco. The National Hurricane Center noted that there was potential for further development,^[36] but conditions were not favorable for development in the short-term, and the disturbance remained poorly consolidated.^[37] However, deep convection became more concentrated on July 12,^[38] and on July 14 Dvorak technique classifications on the disturbance reached high-end tropical depression to low-end tropical storm strength. Based on this, the National Hurricane Center upgraded it to Tropical Depression Five-E at 1500 UTC.^[39] The depression moved west-northwestward and quickly encountered cool sea surface temperatures, increasing wind shear, and outflow from Tropical Storm Cosme. The NHC issued its last advisory late on July 15 after the circulation had become ill-defined and the depression had lost most of its deep convection.^[40]

★ The NHC's Archive on Tropical Depression 5E.

Hurricane Cosme

Two hours after Tropical Depression Five-E was classified, a disturbed area of weather about halfway between Mexico and the Hawaiian islands acquired a surface circulation and sufficient deep convection for the National Hurricane Center to designate it as a tropical depression.^[41] Gradually, the depression became more organized and its circulation became better defined. The NHC upgraded the system to Tropical Storm Cosme on July 15 after analysis with the Dvorak technique estimated that the system had tropical storm force winds.^[42]
On July 16 it strengthened to become the first hurricane of the season^[43], but shortly after that cooler waters and shearing winds initiated a rapid weakening. However, convection made a comeback and Cosme held on to minimal tropical storm strength for over a day, before finally weakening to a depression as it crossed into the Central Pacific. Cosme continued on a west-northwesterly track, moving closer to the Big Island of Hawaii. It passed about 185 miles (295 km) south of the Big Island on July 21 local time, bringing gusts of 30 to 35 knots (35 to 40 mph, 55 to 65 km/h) and heavy rain.^[44]
The final advisory was issued on the evening of July 22 local time as the depression started to dissipate.

★ The NHC's archive on Hurricane Cosme.

★ The CPHC's archive on Tropical Depression Cosme

Tropical Storm Dalila

An area of disturbed weather was first noticed a few hundred miles south-southwest of the Gulf of Tehuantepec on the morning of July 20. The National Hurricane Center noted the possibility of some slow development of the system over the following 48 hours.^[45] 24 hours later, the circulation of the disturbance started to become more consolidated and better defined, leading the NHC to declare the possibility of the formation of a tropical depression.^[46] Late on July 21, the National Hurricane Center initiated advisories on Tropical Depression Seven-E.^[47]
Convection began to flare on the morning of July 23 despite moderate wind shear, and the depression was upgraded to Tropical Storm Dalila, the fourth tropical storm of the season. ^[48] Under constant vertical shear,^[49] Dalila remained a weak tropical storm during the following days. Dalila started to strengthen during the afternoon of July 24 and reached its peak strength as a moderate tropical storm.^[50] Over the next three days, Dalila entered water with sea surface temperatures too cool to support tropical cyclone activity and it ultimately weakened into a tropical depression.^[51]^[52] The final advisory was issued during the morning hours of July 27 as Dalila started degenerating into a remnant low.^[53]

★ The NHC Archive on Tropical Storm Dalila.

Tropical Storm Erick

On July 28, a westward moving area of disturbed weather developed about 950 miles (1530 km) south of the southern tip of Baja California.^[54] A broad low pressure area formed on July 29,^[55] and initially moderate wind shear prevented significant development.^[56] On the morning of July 31, a burst of convection developed in association of a low pressure area;^[57] the convection persisted, and the first advisory on Tropical Depression Eight-E was issued later that afternoon. ^[58] Early on August 1, the depression was upgraded to Tropical Storm Erick based on Dvorak estimates of tropical storm status. ^[59] Continued high amounts of wind shear prevented further strengthening,^[60] and the system dissipated on August 2.

★ The NHC archive on Tropical Storm Erick.

Hurricane Flossie

An area of disturbed weather formed about 600 miles (970 km) south-southeast of Acapulco on August 2. Shower and thunderstorm activity increased in association with a small low pressure area on August 5,^[61] and after continued organization, the National Hurricane Center remarked the system could develop into a tropical depression by early the next day.^[62] Subsequent to another reduction in convection, thunderstorm activity again increased.^[63] Despite marginal upper-level conditions, the system acquired a sufficient amount of organized deep convection for it to be classified Tropical Depression Nine-E late on August 8 while located about 1260 miles (2025 km) west-southwest of the southern tip of Baja California.
Upon first being classified, the depression maintained two ragged hooking bands; situated to the south of a mid-level ridge, it tracked steadily westward.^[64] Later that day the depression was upgraded to Tropical Storm Flossie.^[65] The storm began to develop an eye late on August 9 with good cirrus outflow in all quadrants.^[66] On August 10 the eye became much better defined as the storm strengthened and was upgraded to a hurricane.^[67]^[68]. Hurricane Flossie underwent rapid intensification overnight and became a major hurricane on the morning of August 11^[69] shortly before crossing into the Central Pacific.
In the Central Pacific, the storm continued to track westwards, moving closer to the Hawaiian islands.^[70]^[71] On the afternoon of August 11 Flossie's wind speeds reached an initial peak of 140 mph (220 km/h),^[72] but heading into August 12 increasing vertical shear began restricting outflow and the storm weakened slightly.^[73] By that night outflow had been restored and the storm did not lose intensity as predicted,^[74] and the CPHC issued a hurricane watch the next morning for the Big Island.
However, as the storm moved closer to the Big Island on August 13, the shear began to take a toll on the storm, and it weakened to a low-end category 3 hurricane by late in the day local time, with further weakening expected before it approached the Big Island.^[75] Late on August 14 it was downgraded to a tropical storm,^[76] and on August 16 to a Tropical Depression,^[77].

★ The NHC's Archive on Hurricane Flossie.

★ The CPHC's Archive on Hurricane Flossie.

Tropical Storm Gil

Early on August 29, an area of disturbed weather west of Manzanillo, Colima, Mexico, was designated Tropical Depression Ten-E.^[78] That afternoon, it was upgraded to Tropical Storm Gil, the seventh tropical storm of the season.
^[79] Gil soon weakened as it encountered shearing winds and stable air layering, and it dissipated on September 2 as it moved over cooler waters.
One fatality was reported on August 29, when a 14-year-old boy was swept away by a flood-swollen river in Culiacán, Sinaloa, as parts of the town were flooded by up to 1.5 m.^[80]

★ The NHC archive on Tropical Storm Gil.

Hurricane Henriette

An area of disturbed weather 400 kilometres (250 miles) southeast of Acapulco, Mexico was designated Tropical Depression Eleven-E on August 30.^[81]
The next day it strengthened to become Tropical Storm Henriette^[82], as it moved parallel to the Mexican coast bringing heavy rains. It continued to strengthen as it moved away from Jalisco towards Baja California, and reached hurricane strength on September 4.
Hurricane Henriette made landfall on the tip of the Baja California peninsula near San José del Cabo on September 4^[83]. It was over land for only about six hours before emeging into the Sea of Cortez, still at hurricane strength^[84]. The next day it made final landfall near Guaymas in the state of Sonora^[85].
Rock and mudfalls caused by the heavy rainfall in the Acapulco area caused seven deaths. In Baja California Sur, the threat of the hurricane prompted the evacuations of about 300 people.^[86] Two fishermen were reported killed off the Sonora coast.^[87]

★ The NHC archive on Hurricane Henriette.

Accumulated Cyclone Energy (ACE) Rating

ACE (10⁴kt²) () — Storm:
1	5.30 (17.6)	Flossie	5	1.98	Barbara
2	7.84	Henriette	6	1.18	Gil
3	2.73	Cosme	7	0.613	Alvin
4	2.40	Dalila	8	0.49	Erick
Total: 22.5 (17.6)

The table on the right shows the ACE for each storm in the season. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so storms that last a long time, as well as particularly strong hurricanes, have high ACEs. ACE is only calculated for full advisories on tropical systems at or exceeding 34 knots (39 mph, 63 km/h) or tropical storm strength.
The figures in parenthesis are for storms in the Central Pacific basin west of 140°W; those not in parenthesis are for the Eastern Pacific basin.

Timeline of recent events

August

;August 29
:
★ 8 a.m. PDT (1500 UTC) - 'Tropical Depression Ten-E' forms west of Manzanillo, Mexico
:
★ 2 p.m. PDT (2100 UTC) - Tropical Depression Ten-E is upgraded to 'Tropical Storm Gil'.
;August 30
:
★ 2 p.m. PDT (2100 UTC) - 'Tropical Depression Eleven-E' forms southeast of Acapulco, Mexico.
;August 31
:
★ 5 a.m. PDT (1200 UTC) - Tropical Depression Eleven-E is upgraded to 'Tropical Storm Henriette'.

September

;September 2
:
★ 8 a.m. PDT (1500 UTC) - Last advisory issued for dissipating Tropical Depression Gil.
;September 4
:
★ 2 a.m. PDT (0900 UTC) - Tropical Storm Henriette is upgraded to 'Hurricane Henriette'.
:
★ 1:30 p.m. PDT (2030 UTC) - 'Hurricane Henriette makes landfall just east of Cabo San Lucas, Mexico with 85 mph (140 km/h) winds.'
;September 5
:
★ 5 p.m. PDT (0000 UTC September 6) - 'Hurricane Henriette makes a second landfall near Guaymas, Mexico.'
:
★ 8 p.m. PDT (0300 UTC September 6) - Hurricane Henriette is downgraded to a tropical storm.
;September 6
:
★ 2 a.m. PDT (0900 UTC) - Tropical Storm Henriette is downgraded to a tropical depression, and prediction responsibility passed to the HPC.
:
★ 8 a.m. PDT (1500 UTC) - Tropical Depression Henriette is downgraded to a remnant low.

Storm names

The following names will be used for named storms that form in the northeast Pacific in 2007. This is the same list that was used in the 2001 season, except for Alvin, which replaced Adolph, which was retired due to political sensitivities. The name Alvin was used for a storm for the first time this year. Storms that form in the central Pacific are given names from a sequential list; if any are used, they will be mentioned separately.

★ Alvin ★ Barbara ★ Cosme ★ Dalila ★ Erick ★ Flossie ★ Gil ★ Henriette	★ ★ ★ ★ ★ ★ ★ ★	★ ★ ★ ★ ★ ★ ★ ★

For the central Pacific Ocean, four consecutive lists are used, with the names used sequentially until exhausted, rather than until the end of the year, due to the low number of storms each year. The next name used from the Central Pacific list will be ''Kika''.
Retired names, if any, will be announced by the WMO in the spring of 2008.

References

External links

★ National Hurricane Center's Eastern Pacific Tropical Weather Outlook - updated four times daily

★ National Hurricane Center

★ National Hurricane Center's 2007 Advisory Archive

★ Central Pacific Hurricane Center

★ NRL hurricane page - Naval Research Laboratory page with extensive archives on individual storms

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