October 2010 Climate Report

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

October 2010 Highlights:

Temperatures across Puerto Rico ranged from 57ºF in Toro Negro on the 18^th of October to 96ºF in Gurabo on the 18^th of the month. Temperatures across the U.S. Virgin Islands ranged from 71ºF, October 28^th at the Cyril E. King airport on Saint Thomas, to 89ºF, recorded at Red Hook Bay on Saint Thomas on the 11^th of October. Other notable temperatures for October 2010 are listed below:

Other Notable October 2010 High’s:	Other Notable October 2010 Low’s:
94ºF in Rio Piedras on October 25^th	63ºF in Maricao on October 19^th
94ºF in Ponce on October 26^th	63ºF in Aibonito on October 10^th
94ºF in Palmarejo on October 21^st	64ºF in Lajas on October 25^th
93ºF in Trujillo Alto on October 17^th	65ºF at the Arecibo Observatory on October 20^th
93ºF in Aguadilla on October 9^th	66ºF in Ponce on October 25^th
92ºF in San Juan, Mayaguez, Guayama and Juncos	66ºF in Gurabo on October 25^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 October was 11.10”, which fell in Jajome Alto over the 24 hour period ending at 8am October 8^th. The highest weekly rainfall across Puerto Rico also occurred in Jajome Alto, where 21.51” of rain accumulated the week ending October 8^th. Across the U.S. Virgin Islands, the highest 24-hour precipitation total fell at Coral Bay on Saint John, where 8.50” fell over the 24 hour period ending at 8 am on October 6^th. For the week ending October 8^th, 21.52” of rain fell at Red Hook Bay on Saint Thomas, representing the highest weekly rainfall across the U.S. Virgin Islands for the month of October.

Year to Data Rainfall across Puerto Rico and Departure from normal.

Figure 1A – Island wide averaged precipitation (and normals) - by week - for the weeks beginning on January 2nd and ending on October 29th, 2010

October 2010 Rainfall and Raingage composite of Precipitation across Puerto Rico.

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

Monthly Weather Summary:

Afternoon convection was the rule during the first few days of October as a result of daytime heating and sea breeze convergence. The steering flow focused this shower activity along the north central and northwestern sections of Puerto Rico each afternoon. This scenario changed around the 4^th of the month as a broad area of low pressure (which developed into hurricane Otto) combined with an upper level low to produce an active/wet pattern across the local islands through the second week of the month. Then, generally fair weather prevailed across the local islands through the end of the month with limited afternoon convection across western Puerto Rico each afternoon. By the end of the month, a very active tropical wave to our southeast became hurricane Tomas. This system tracked south of the area leaving hazardous and choppy sea conditions across the Caribbean waters.

Statistically, October 2010 was above normal in terms of both temperatures and precipitation in San Juan. At the Luis Muñoz Marin International Airport in San Juan, the monthly precipitation total of 7.86” was 2.80” above normal. A record 1.82 inches of rainfall was set on the 29^th, surpassing the 1.19 inches of rainfall accumulated on the same date back in 1961. In terms of temperature, the average temperature was 0.8 degrees above normal in October, marking the 17^th consecutive month of above normal temperatures recorded in San Juan. The highest monthly temperature in San Juan reached 92 degrees on both October 10^th and 21^st, and the lowest temperature fell to 73 degrees on October 28^th.

Across the U.S. Virgin Islands, October 2010 was above normal in terms of precipitation and below normal in terms of temperature. At the Cyril E. King Airport on St Thomas, the monthly precipitation total of 16.20” was 10.63” above normal. This represented the wettest October on Saint Thomas since 1953 and the 3^rd wettest month on record. In terms of temperature, the average temperature was 2.4 and 2.2 degrees below normal for St Thomas and St Croix respectively. The highest monthly temperature reached 88 degrees on October 2^nd at Christiansted Airport on St Croix, and the lowest temperature fell to 71 degrees on October 28^that St Thomas.

October 2010 Statistics:

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”

October 2010 Observations:

	San Juan	Saint Thomas	Saint Croix
High:	88.0ºF (+0.5ºF)	85.0ºF (-4.5ºF)	85.5ºF (-3.0ºF)
Low:	76.8ºF (+1.2ºF)	76.0ºF (-0.2ºF)	74.6ºF (-1.3ºF)
AvgT:	82.4ºF (+0.8ºF)	80.5ºF (-2.4ºF)	80.0ºF (-2.2ºF)
Pcpn:	7.85” (+2.79”)	16.20” (+10.63”)	8.90” (+3.68”)

October 2010 Extremes:

	San Juan	Saint Thomas	Saint Croix
High:	92ºF – October 10th & 21st	87ºF – October 4th & 23rd	88ºF – October 2nd
Low:	73ºF – October 28th	71ºF – October 28th	72ºF – October 20th

October Historical Statistics:

Highest October Temperatures on record:

San Juan	Saint Thomas	Saint Croix
98ºF – October 9^th, 1981	97ºF – October 14^th, 1994*	98ºF – October 1^st, 1972
97ºF – October 13^th,		97ºF – October 11^th, 1995
1987*		95ºF – October 4^th, 1972
*Most recent occurrence	*Most recent occurrence	94ºF – October 17^th, 1972*
		*Most recent occurrence

Lowest October Temperatures on record:

San Juan	Saint Thomas	Saint Croix
67ºF – October 10^th, 1959	66ºF – October 27^th- 29^th, 2007	65ºF – October 22^nd- 23^rd, 1983, October 31^st, 1975, October 26^th, 29^th, 30^th & 31^st, 1974
70ºF – October 30^th, 2001*	68ºF – October 15^th, 1954	66ºF – October 10^th, 1982 & October 8^th, 1977
	69ºF – October 10^th, 1956 &
*Most recent occurrence	October 4^th, 1954	*Most recent occurrence

Wettest Octobers:

San Juan	Saint Thomas	Saint Croix
15.06” October 1970	16.20” October 2010	16.20” October 1977
11.94” October 2005	12.49” October 2005	12.95” October 1990
11.25” October 2006	12.45” October 1974	11.79” October 1954

Driest Octobers:

San Juan	Saint Thomas	Saint Croix
1.17" October 1979	1.77” October 1953	1.05” October 1964
1.63" October 1963	2.00” October 1988	1.10” October 2002
1.74" October 1992	2.21” October 1979	1.23” October 1960

2000-2010 Decade in Review:

October 2010 marked the 17^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. Temperatures have already cooled off somewhat across the U.S. Virgin Islands, where October temperatures were over 2 degrees below normal at the International Airports of both Saint Thomas and Saint Croix.

Thanks to another abnormally wet month across the local islands, largely due to record rainfall associated with Hurricane Otto, 2010 remains on track to be the wettest year in San Juan since record keeping began. By the end of the month, 7.86” of rainfall had accumulated at the Luis Muñoz Marin International Airport in San Juan, with 74.08” of rain falling since the first of the year (nearly three feet above the normal 40.02” 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 October 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 October High Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*88.0ºF*	*88.2ºF*	*88.6ºF*	*89.2ºF*	*88.3ºF*	*87.5ºF*	*87.4ºF*

Decadal October Low Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*76.8ºF*	*76.4ºF*	*76.1ºF*	*75.5ºF*	*76.4ºF*	*74.2ºF*	*72.6ºF*

Decadal October Average Temperatures:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*82.4ºF*	*82.3ºF*	*82.4ºF*	*82.4ºF*	*82.4ºF*	*80.8ºF*	*80.0ºF*

Decadal October Precipitation:

2010	2000’s	1990’s	1980’s	1970’s	1960’s	1950’s
*7.85”*	*6.20”*	*4.48”*	*5.58”*	*6.29”*	*4.85”*	*7.15”*

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

Decadal October Temperature for San Juan Puerto Rico for the month of October.

Figure 2 - Temperature deviations for San Juan, PR

Temperatures for October on Saint Thomas for the 2000's.

Figure 3 - Temperature deviations for Saint Thomas, VI

October 2000's temperatures for Saint Croix.

Figure 4 - Temperature deviations for Saint Croix, VI

October 2000's precipitation for San Juan, Saint Croix and Saint Thomas.

Figure 5 - October 2000's precipitation deviations from normal

Year to date percent of normal precipitation for San Juan, Saint Thomas and Saint Croix.

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

Looking ahead toward the month of November:

Looking ahead, November is the wettest month of the year in San Juan (an average of 6.17” of rain falls at the Luis Muñoz International Airport in San Juan each November). The wettest November on record was November 1979, when 15.96” of rain fell in San Juan, and the driest November on record was November 1980, when only 1.91” of rainfall was recorded. The mean temperature at the Luis Muñoz International Airport in San Juan for November is 79.6ºF, making November the 6^th coolest month of the year. See the table below for average November temperatures and precipitation from across Puerto Rico and the U.S. Virgin Islands.

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

	San Juan	Saint Thomas	Saint Croix
High:	85.1ºF	87.8ºF	87.0ºF
Low:	74.0ºF	74.9ºF	74.3ºF
AvgT:	79.6ºF	81.4ºF	80.7ºF
Pcpn:	6.17”	5.28”	5.55”

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

The sun rises at 6:24 am AST and sets at 5:52 pm AST, in San Juan, Puerto Rico on November 1^st. This represents a total of 11 hours and 28 minutes of daylight. By November 30^th, the sun will rise at 6:40 am AST and set at 5:46 pm AST, providing a total of 11 hours and 6 minutes of daylight, or a total decrease in 22 minutes over the course of the month.

At Charlotte Amalie on Saint Thomas, the sun will rise at 6:19 am AST and set at 5:47 pm AST on the 1^st of the month. By the end of the month, the sun will rise at 6:35 am AST and set at 5:42 pm AST, representing a total decrease in daylight of 21 minutes over the course of the month.

For the month of November, a full moon will be observed on the 21^st of the month. There will also be a new moon on the 6^th of the month. The last quarter of the moon will be observed on the 28^th of the month and the first quarter of the new moon will be observed on the 13^th of the month.

Links to additional sunrise/sunset data, phases of the moon, as well as tide data can all be found by going to the climate portion of the National Weather Service San Juan homepage (http://www.weather.gov/climate/index.php?wfo=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

National Weather Service Weather Forecast Office