September 2010 Climate Report

September 2010 Climate Report for Puerto Rico and the U.S. Virgin Islands

September 2010 Highlights:

Temperatures across Puerto Rico ranged from 60ºF in Cerro Maravilla on the 5^th of September to 97ºF in Ponce, also on the 5^th of September. Temperatures across the U.S. Virgin Islands ranged from 72ºF, September 14^th at the Christiansted airport on Saint Croix, to 91ºF, recorded at both the Cyril E. King Airport on Saint Thomas and Fort Christiansted on Saint Croix, on the 19^th and 18^th of the month respectively. Other notable temperatures for September 2010 are listed below:

Other Notable September 2010 High’s:	Other Notable September 2010 Low’s:
96ºF in Guayama on September 16^th	61ºF in Toro Negro on September 3^rd
96ºF in Gurabo on September 26^th	63ºF in Maricao on September 6^th
95ºF in Palmarejo on September 1^st	64ºF in Trujillo Alto on September 25^th
94ºF in Corozal on September 2^nd	65ºF in Aibonito on September 26^th
94ºF in Lajas on September 16^th	65ºF on Magueyes Island on September 30^th
94ºF in San Juan on September 2^nd	65ºF in Arecibo on September 27^th

^{*If multiple occurrences, all dates above reflect the latest occurrence of the month.}

The highest 24-hour precipitation total across Puerto Rico for the month of September was 3.24”, which fell at the Guajataca Dam over the 24 hour period ending at 8am September 13^th. The highest weekly rainfall across Puerto Rico occurred in Palmarejo, where 6.80” of rain accumulated the week ending September 3^rd. Across the U.S. Virgin Islands, the highest 24-hour precipitation total fell at Fort Christiansted on Saint Croix, where 1.56” fell over the 24 hour period ending at midnight on September 18^th. For the week ending September 3^rd, 4.27” of rain fell at Montpellier on Saint Croix, representing the highest weekly rainfall across the U.S. Virgin Islands for the month of September.

Precipitation accumulation from coop stations around Puerto Rico January through September 2010.

Figure 1A – Island wide averaged precipitation (and normals) - by week - for the weeks beginning on January 2nd and ending on October 1, 2010

Graphical precipitation estimate for September 2010 derived from the combination of radar and rain gage data.

Figure 1B – Graphical Display of September 2010 precipitation across Puerto Rico and the U.S. Virgin Islands derived from a combination of rain gage and radar data.

Monthly Weather Summary:

September 2010 began with hurricane Earl located well northwest of the local islands while tropical storm Fiona was situated east of the Leeward Islands. No major problems associated with these two cyclones were reported across the forecast area. The following days, afternoon convection prevailed as a result of deep tropical moisture across the region, local effects as well as some ventilation associated with an upper level low situated to the northeast of the local islands. By the second week of the month, the remnants of former tropical storm Gaston tracked south of the local islands as a drier air mass moved into the area. Days after, another tropical system caught the attention of residents across the northeastern Caribbean, as major hurricane Igor was forecasted to pass less than 500 nautical miles from the local islands. After hurricane Igor passed to the northeast of the local islands, a high pressure system built across the east central Atlantic and subsidence around Igor prevailed across the local area. By the end of the month, a surge of deep moisture from the southeast Caribbean reached the local area, increasing shower and thunderstorms activity.

Statistically, September 2010 was above normal in terms of both temperatures and precipitation. At the Luis Muñoz Marin International Airport in San Juan, the monthly precipitation total of 8.86” was 3.26” above normal. In terms of temperature, the average temperature was 1.0 degrees above normal in September, marking September the 16^th consecutive month of above normal temperatures recorded in San Juan. The high temperature in San Juan reached 94 degrees on September 2^nd, and the low temperature fell to 76 degrees on September 11^th, 21^st, and 24^th.

September 2010 Statistics:

Average September Temperatures/Precipitation (NCDC 1971-2000 averages):

	San Juan	Saint Thomas	Saint Croix
High:	87.8ºF	90.2ºF	89.2ºF
Low:	76.5ºF	76.9ºF	76.8ºF
AvgT:	82.2ºF	83.6ºF	83.0ºF
Pcpn:	5.60”	5.34”	5.36”

September 2010 Observations:

	San Juan	Saint Thomas	Saint Croix
High:	88.4ºF (+0.6ºF)	89.0ºF (-1.2ºF)	87.8ºF (-1.4ºF)
Low:	78.1ºF (+1.6ºF)	80.1ºF (+3.2ºF)	76.0ºF (-0.8ºF)
AvgT:	83.2ºF (+1.0ºF)	84.6ºF (+1.0ºF)	81.9ºF (-1.1ºF)
Pcpn:	8.86” (+3.26”)	2.69” (-2.65”)	3.75” (-1.61”)

September 2010 Extremes:

	San Juan	Saint Thomas	Saint Croix
High:	94ºF – September 2^nd	91ºF – September 24^th	90ºF – September 2^nd
Low:	76ºF – September 21^st & 24^th	78ºF – September 26^th & 30^th	72ºF – September 14^th

September Historical Statistics:

Highest September Temperatures on record:

San Juan	Saint Thomas	Saint Croix
97ºF – September 21^st, 1981	98ºF – September 1^st, 5^th &	95ºF – September 24^th, 1983
96ºF – September 18^th,	28^th, 1993	& September 12^th, 15^th, 18^th
1995*	97ºF – September 5^th, 1995*	& 25^th, 1972
*Most recent occurrence	*Most recent occurrence	94ºF – September 18^th, 1983*
		*Most recent occurrence

Lowest September Temperatures on record:

San Juan	Saint Thomas	Saint Croix
69ºF – September 6^th & 15^th,	68ºF – September 11^th, 1994,	65ºF – September 8^th, 1982
1960	September 8^th, 1979 &	66ºF – September 24^th, 1975
70ºF – September 9^th, 1998*	September 11^th, 1972	67ºF – September 7^th, 1982*
*Most recent occurrence	69ºF – September 9^th, 1980	*Most recent occurrence

Wettest Septembers:

San Juan	Saint Thomas	Saint Croix
15.15” September 1996	14.94” September 1953	21.39” September 1979
14.83” September 1989	13.89” September 2004	19.15” September 1996
11.44” September 1976	12.86” September 2008	9.80” September 1953

Driest Septembers:

San Juan	Saint Thomas	Saint Croix
1.73” September 1987	1.08” September 1986	1.07” September 1981
1.78” September 2006	1.42” September 1987	1.42” September 2006
1.93” September 1961	1.62” September 1983	1.64” September 2001

2000-2010 Decade in Review:

September 2010 marked the 16^th consecutive month of above normal temperatures in San Juan. Thanks to a recent study on El Niño and the Southern Oscillation, it was noted that this string on abnormally warm temperatures was likely influenced by a strong El Niño which persisted across the tropical Pacific through April 2010. Additionally, now with a La Niña advisory in effect, it is thought that this string of abnormally warm temperatures may come to an end in the upcoming months.

Thanks to another abnormally wet month across the local islands, 2010 remains on track to be the wettest year in San Juan since record keeping began. By the end of the month, 8.86” of rainfall had accumulated at the Luis Muñoz Marin International Airport in San Juan, with 66.22” of rain falling since the first of the year (more than two and a half feet above the normal 34.96” that accumulates in San Juan by this date).

For a look at temperature and precipitation deviations for San Juan, Saint Thomas and Saint Croix from their NCDC averages, see Figures 2 to 6 below. Additionally, a summary of the September 2010 data for San Juan along with the previous 6 decades of data for San Juan has also been included below.

Decadal Observations for San Juan, Puerto Rico:

Decadal September High Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*88.4ºF*	*89.2ºF*	*89.3ºF*	*89.9ºF*	*88.4ºF*	*87.8ºF*	*88.4ºF*

Decadal September Low Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*78.1ºF*	*77.2ºF*	*76.9ºF*	*76.6ºF*	*76.9ºF*	*74.9ºF*	*73.6ºF*

Decadal September Average Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*83.2ºF*	*83.2ºF*	*83.1ºF*	*83.2ºF*	*82.7ºF*	*81.4ºF*	*81.0ºF*

Decadal September Precipitation:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*8.86”*	*5.86”*	*6.44”*	*4.61”*	*6.02”*	*5.83”*	*5.02”*

* Records for San Juan began on January 1^st, 1956

San Juan Temperatures for the month of September in the 2000's.

Figure 2 - Temperature deviations for San Juan, PR

Saint Thomas September temperatures for the 2000's.

Figure 3 - Temperature deviations for Saint Thomas, VI

Saint Croix September temperatures for the 2000's.

Figure 4 - Temperature deviations for Saint Croix, VI

San Juan, Saint Thomas and Saint Croix precipitation for the month of September in the 2000s.

Figure 5 - September 2000's precipitation deviations from normal

2010 precipitation deviation from normal for San Juan, Saint Thomas and Saint Croix.

Figure 6 - January - September 2010 precipitation deviations for San Juan, Saint Thomas, and Saint Croix

Looking ahead toward the month of October:

Looking ahead, the month of October is the second wettest month of the year across Puerto Rico as a whole, and October is the 5^th wettest month of the year in San Juan (an average of 5.06” of rain falls at the Luis Muñoz International Airport in San Juan each October). The wettest October on record was October 1970, when 15.06” of rain fell in San Juan, and the driest October on record was October 1979, when only 1.17” of rainfall was recorded. The mean temperature at the Luis Muñoz International Airport in San Juan for October is 81.6ºF, making October the 5^th warmest month of the year. While the peak of hurricane season has passed, the updated August 2010 outlook for the remainder of the 2010 Atlantic hurricane season continues to indicate nearly a 100% chance of a normal or above normal hurricane season which ends on November 30^th. The official discussion from the climate prediction center can be viewed at: http://www.cpc.noaa.gov/products/outlooks/hurricane.shtml

Average October Temperatures/Precipitation (NCDC 1971-2000 averages):

	San Juan	Saint Thomas	Saint Croix
High:	87.5ºF	89.5ºF	88.5ºF
Low:	75.6ºF	76.2ºF	75.9ºF
AvgT:	81.6ºF	82.9ºF	82.2ºF
Pcpn:	5.06”	5.57”	5.22”

Moon/Sun/Tide Data for the month of October:

The sun rises at 6:15 am AST and sets at 6:13 pm AST, in San Juan, Puerto Rico on October 1^st. This represents a total of 11 hours and 58 minutes of daylight. By October 31^st, the sun will rise at 6:24 am AST and set at 5:52 pm AST, providing a total of 11 hours and 28 minutes of daylight, or a total decrease in 30 minutes over the course of the month.

At Charlotte Amalie on Saint Thomas, the sun will rise at 6:10 am AST and set at 6:08 pm AST on the 1^st of the month. By the end of the month, the sun will rise at 6:19 am AST and set at 5:48 pm AST, representing a total decrease in daylight of 29 minutes over the course of the month.

For the month of October, a full moon will be observed on the 22^nd of the month. There will also be a new moon on the 7^th of the month. The last quarter of the moon will be observed on the 30^th of the month and the first quarter of the new moon will be observed on the 14^th of the month.

Links to additional sunrise/sunset data, phases of the moon, as well as tide data can all be found by clicking on the climate link of the National Weather Service San Juan homepage (www.srh.noaa.gov/sju) and then clicking on the Astronomical tab.

Click here to return to the unique local data/records section of the NWS San Juan climate page

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