FXPN30 KWNC 251550
PMDEPH
Eastern North Pacific Hurricane Season Outlook 2023
NWS Climate Prediction Center College Park MD
1100 AM EDT Thu 25 May 2023
 
 
Note: figures mentioned in the discussion are available
on the internet at http://www.cpc.ncep.noaa.gov
 
NOAA 2023 Eastern Pacific Hurricane Season Outlook Issued 25
May 2023

This 2023 eastern Pacific Hurricane Season Outlook is an
official product of the National Oceanic and Atmospheric
Administration /NOAA/ Climate Prediction Center /CPC/, and is
produced in collaboration with hurricane experts from NOAAs
National Hurricane Center /NHC/ and the Hurricane Research
Division /HRD/. The eastern Pacific hurricane region covers
the eastern North Pacific Ocean east of 140 degW and north
of the equator.

Interpretation of NOAAs eastern Pacific hurricane season
outlook This outlook is a general guide to the expected overall
activity during the upcoming hurricane season. It is not a
seasonal hurricane landfall forecast, and it does not imply
levels of activity for any particular location.

Preparedness Hurricane-related disasters can occur during any
season, even for years with low overall activity. It only takes
one hurricane /or even a tropical storm/ to cause a disaster. It
is crucial that residents, businesses, and government agencies
of coastal and near-coastal regions prepare for every hurricane
season regardless of this, or any other, seasonal outlook. The
Federal Emergency Management Agency /FEMA/, the NHC, the Small
Business Administration, and the American Red Cross all provide
important hurricane preparedness information on their web sites.

NOAA does not make seasonal hurricane landfall predictions NOAA
does not make seasonal hurricane landfall predictions. Hurricane
landfalls are largely determined by the weather patterns in
place as the hurricane approaches, which are predictable when
the storm is within several days of making landfall.

Nature of this outlook and the "likely" ranges of activity
This outlook is probabilistic, meaning the stated "likely"
ranges of activity have a certain likelihood of occurring. The
seasonal activity is expected to fall within these ranges in
7 out of 10 seasons with similar conditions and uncertainties
to those expected this year. They do not represent the total
possible ranges of activity seen in past similar years.

This outlook is based on climate model forecasts, and on
predictions of large-scale climate factors and conditions
that are known to strongly influence seasonal eastern Pacific
hurricane activity. The outlook also takes into account
uncertainties inherent in such climate outlooks.

Sources of uncertainty in this seasonal outlook 
1. Predicting El Nino and La Nina events /also called El
Nino-Southern Oscillation, ENSO/ and specific impacts on 
eastern Pacific hurricane activity is an ongoing scientific 
challenge facing climate scientists today. Such forecasts
made during the spring generally have more uncertainty than
those made closer to the peak of hurricane season
/July-September: JAS/..

2. Uncertainty as to whether the eastern Pacific has shifted
to a long-term low-activity era, or that the recent quiescent
period will be short lived and there will be a return to the
high activity era that lasted from 2014-2019.

3. Predicting the combined impacts associated with the Pacific
Decadal Oscillation /PDO/, ENSO, and the Atlantic Multidecadal
Oscillation /AMO/ remains a challenge, especially when they
have different temporal variability that sometimes results in
competing influences.

4. Many combinations of named storms, hurricanes, and major
hurricanes can occur for the same general set of climate
conditions. For example, one cannot know with certainty
whether a given climate signal will be associated with several
short-lived storms or fewer longer-lived storms with greater
intensity.

5. Shorter-term weather patterns that are unpredictable
on seasonal time scales can sometimes develop and last for
weeks or months within a season, possibly affecting seasonal
hurricane activity.


2023 Eastern Pacific Hurricane Outlook Summary

a. Predicted Activity NOAAs 2023 eastern Pacific Hurricane
Season Outlook /Fig. 1/ indicates an above-normal season
is most likely /55 percent chance/. There is a 35 percent
chance of a near-normal season and only a 10 percent
chance of a below-normal season. See NOAA definitions
/https://www.cpc.ncep.noaa.gov/products/Epac_hurr/Background.html/
of above-, near-, and below-normal seasons. The eastern Pacific
hurricane region covers the eastern North Pacific Ocean east
of 140 degW and north of the equator.

The 2023 outlook calls for a 70 percent probability for each
of the following ranges of activity:
 14-20 Named Storms
 7-11 Hurricanes
 4-8 Major Hurricanes
 Accumulated Cyclone Energy /ACE/ range of 90 percent-155
 percent of the median.

The activity is expected to fall within these ranges in
70 percent of seasons with similar climate conditions and
uncertainties to those expected this year. These ranges
do not represent the total possible activity seen in past
similar years. The predicted ranges are centered above the
1991-2020 averages of 15 named storms, 8 hurricanes, and 4
major hurricanes.

The eastern Pacific hurricane season officially runs from May
15th through November 30th. The peak months of the season are
July-September /JAS/.

There will be no further updates to this outlook.

b. Reasoning behind the outlook Two climate factors are expected
to contribute to an above-normal 2023 hurricane season across
the eastern /and central/ Pacific hurricane basins, as follows:

1/ The latest monthly sea-surface temperature /SST/ anomalies
/Fig. 2/ reflect ENSO-neutral conditions, on the path to
the predicted El Nino, and a negative PDO structure, while
also showing the North Atlantic SSTs as above-normal for much
of the basin. Dissimilar from the past 2 years, positive SST
anomalies are measured in the far tropical eastern Pacific near
Peru. However, SST anomalies in the regions where many of the
tropical storms and hurricanes form /110 degW - 140 degW/
are still below normal. The predicted /Fig. 3/ SST anomaly
patterns indicate above-average SSTs across the eastern
Pacific hurricane region, though there is some evidence of
influence from the negative PDO related circulation pushing
cooler waters southward. The cooler waters are expected to
occur mainly west of 110 degW. SSTs across the Atlantic Main
Development Region /MDR/ are above normal, and warmer than
last year at this time. Historically, this combination tends
to be associated with near- or above-normal hurricane activity
in the eastern Pacific, as El Nino does tend to have a larger
influence, though El Nino concurrent with a negative PDO is
not that common /39 of 880 months since Jan 1950/.

2/ The most recent forecast from the NOAA Climate Prediction
Center /Fig. 4/ indicates El Nino conditions are likely through
the hurricane season. The ENSO influence on eastern Pacific
hurricane activity is highly dependent upon the background
SST patterns across the eastern Pacific hurricane region and
the Atlantic MDR. The combination of El Nino and above-normal
temperatures in the Atlantic MDR tends to favor increased
eastern Pacific hurricane activity, often resulting in a
near- or above-normal hurricane season. El Nino combined with
a warm Atlantic MDR and negative PDO, can result in a wide
range of outcomes, centered just slightly above the 1991-2020
averages. El Nino and a high activity era in the East Pacific,
which we may be entering, results in even high named storm,
hurricane, major hurricane, and ACE totals.

DISCUSSION 1. Expected 2023 activity

NOAAs 2023 eastern Pacific Hurricane Season Outlook /Fig. 1/
indicates an above-normal season is most likely /55 percent
chance/. There is a 35 percent chance of a near-normal season
and a 10 percent chance of a below-normal season.

The 2023 eastern Pacific hurricane season is predicted to
produce /with a 70 percent probability for each range/ 14-20
named storms, of which 7-11 are expected to become hurricanes,
and 4-8 of those are expected to become major hurricanes. These
ranges are centered above the 1991-2020 seasonal averages of
15 named storms, 8 hurricanes, and 4 major hurricanes.

An important measure of the total seasonal activity is NOAAs
Accumulated Cyclone Energy /ACE/ index /Fig. 5/, which accounts
for the combined intensity and duration of named storms and
hurricanes during the season. This 2023 outlook indicates a
70 percent chance that the ACE range will be 90 percent-155
percent of the median. An ACE value of 80 percent-120 percent
of the median indicates a near-normal season. Values above
this range reflect an above-normal season, and values below
this range reflect a below-normal season.

Predictions of the location, number, timing, and intensity of
hurricane landfalls are ultimately related to the daily weather
patterns which determine storm genesis locations and steering
patterns. These patterns are not predictable weeks or months in
advance. As a result, it is currently not possible to reliably
predict the number or intensity of landfalling hurricanes at
these extended ranges, or whether a given locality will be
impacted by a tropical storm or hurricane this season.


2. Science behind the Outlook

NOAAs eastern Pacific Hurricane Season Outlook is based on
predictions of the main climate factors and their associated
relationships to the hurricane season, as well as direct
output from numerical models. The outlook is based on
extensive monitoring, analysis, research activities, a suite
of statistical prediction tools, and dynamical models. The
dynamical model predictions come from the NOAA Climate Forecast
System /CFS/, NOAA Geophysical Fluid Dynamics Lab /GFDL/ HiFLOR
and SPEAR-MED modes, the North American Multi-Model Ensemble
/NMME/, the United Kingdom Met Office /UKMET/ GloSea6 model,
and the European Centre for Medium-Range Weather Forecasting
/ECMWF/ Seas5 model. ENSO forecasts are also provided from
the NMME dynamical models contained in the suite of Nino 3.4
SST forecasts /Fig. 6/, which is compiled by NOAAs CPC.

NOAAs 2023 eastern Pacific Hurricane Season Outlook reflects
two main factors, as follows:

1/ The predicted SST anomaly patterns /Fig. 3/ indicate near to
above-average SSTs across the eastern Pacific hurricane region,
and above-average SSTs across the Atlantic MDR. In the region
where most tropical cyclones form in the Eastern Pacific, SSTs
are currently below normal. The uncertainty in the outlooks for
the SSTs to reverse sign is reflected in the relatively moderate
probabilities in this outlook. For the Pacific, these conditions
also project onto the negative phase of the Pacific Decadal
Oscillation /PDO/ /Fig. 8/ and also onto the warm /positive/
phase of the Atlantic Multidecadal Oscillation /AMO/ and the
Atlantic Meridional Mode /AMM/ /Fig. 9/. Historically, this
combination of climate patterns tends to be associated with
near-normal or above-normal activity in the eastern Pacific
hurricane region. The exact interplay and net result of
the interbasin relationships is uncertain and still a focus
of ongoing research, and that uncertainty is reflected in
the relatively moderate probabilities in this outlook. These
conditions do not come about often, with only 39 of 880 months
since Jan 1950 having an El Nino during JAS /JAS Nino3.4 <
-0.5 degC/ combined with a PDO < -0.1 during JAS. The exact
interplay and net result of the interbasin relationships is
uncertain and still a focus of ongoing research.

2/ The most recent forecast from the CPC /Fig. 4/ favors El
Nino /91 percent chance/ conditions during JAS with negligible
odds for the development of La Nina /~0 percent/. Historically,
El Nino events usually mean more activity for the East Pacific,
and often for the Central Pacific. During high activity eras in
the East Pacific, typically associated with low activity eras
in the Atlantic - which we are not in now, ENSO-neutral can
produce about as many storms as El Nino. The conclusion the
team drew from that is that during uncertain eras, ENSO can
have an outsized impact, but that other factors can increase
the uncertainty.

a. El Nino favored

ENSO-neutral conditions are present at this time. As of May
12, 2023, the weekly SSTs are currently near average across
the central and eastern equatorial Pacific /Fig. 7/, and the
SST index for the Nino 3.4 region is +0.4 degC /Fig. 7/. The
weekly Nino 3.4 index had been between -0.5 degC and +0.5 degC
since February of 2023. The Nino 3.4 index has shown a
significant warming trend since December 2022. The wind and
outgoing longwave radiation patterns over the central Pacific
are also reflecting a breakdown of the atmospheric response to
La Nina forcings, and more influence from intraseasonal modes.

Looking forward, the official CPC ENSO outlook /Fig.4/ indicates
a very high confidence in the development of El Nino conditions
during JAS 2023. The model-predicted SST anomalies in the
Nino 3.4 region /Fig. 6/ generally indicate El Nino /Nino
3.4 index greater than +0.5 degC/ conditions throughout the
hurricane season. The dynamical model average /dashed black
line/ indicates El Nino through the summer and autumn of 2023,
with only one modeling system indicating ENSO-neutral. When
using a larger pool of models, that includes multiple dynamical
models, multiple statistical models, and unique combinations
21 of 24 models indicate El Nino, with 3 indicating warm but
neutral conditions.

NOAAs Climate Forecast System /CFS/ and the North American
Multi-Model Ensemble /NMME/ are predicting El Nino. The CFS
predicts below-normal shear over the East Pacific /Fig. 10,
left/ while the NMME predicts /Fig 10, right/ well above-normal
shear for the same region. The shear predicted by the NMME this
year is stronger than what was predicted last year /further
from climatology/ for much of the hurricane development region
of the eastern Pacific.

b. Eastern North Pacific high- and low-activity eras

In addition to year-to-year fluctuations, eastern Pacific
hurricane activity exhibits strong variability on decadal and
multi-decadal time scales /Fig. 5/. Periods of decreased
activity /such as 1971-1981 and 1995-2013/ are called
low-activity eras, and periods of increased activity /such
as 1982-1994 and 2014-2019/ are called high-activity eras,
though its not clear if the recent lull is indeed an end to
a high-activity era, or simply a pause, given 2022 having
an above-normal year. These are different from the high-
and low-activity eras in the Atlantic hurricane region. The
differences in seasonal activity between these two eras for
the eastern Pacific are considerable /Fig. 11/. High-activity
eras average about 4.5 more named storms, 2.8 more hurricanes,
2.3 more major hurricanes, and 56 percent more ACE, than
low-activity eras. During high-activity eras, above-normal
seasons occur about three times more frequently /63 percent
of seasons compared to 20 percent/, and below-normal seasons
are about four times less frequent /11 percent compared to
43 percent/.

High- and low-activity eras in the eastern Pacific hurricane
region are strongly related to global patterns of SST anomalies
that change slowly and last for many years. It is upon these
patterns that the inter-annual ENSO signal overlays. One
such pattern is called the Pacific Decadal Oscillation /PDO/
/Fig. 8/. The PDO spans most of the North Pacific Ocean,
and is associated with decadal fluctuations in hurricane
activity. The positive /negative/ phase of the PDO tends to
be associated with high- /low-/ activity eras. Another SST
pattern is the Atlantic Multi-decadal Oscillation /AMO/, and
when linked to wind patterns can be more broadly described
as Atlantic Multidecadal Variability /AMV/, measured through
the Atlantic Meridional Mode /AMM/. The cold /warm/ phase of
the AMO increases the likelihood of a high- /low-/ activity
era. The AMO helps to explain the inverse relationship in
activity between the eastern Pacific and Atlantic basins, with
a warm AMO/positive AMM favoring increased Atlantic activity
and decreased eastern Pacific activity. The AMO is positive
this year with warm SSTs  in the North Atlantic.

The 1982-1994 high-activity era was associated with a cold AMO
and a positive PDO, while the period from 2014-2019 exhibited
higher activity and primarily featured a strong positive PDO,
there is uncertainty about the classification of the activity
regime in the Pacific. Such a short period of years would
not define an activity era. The relative lull in activity
during 2020 and 2021 could just be more consistent with
repeat La Nina events overriding the multi-year signals. The
intervening 1995-2013 low-activity era featured a warm AMO and
negative PDO. Of the years when the August PDO was negative,
approximately 70 percent of those years were near normal or
below normal for activity /16 of 22 since 1971/. The current
value of the PDO is -1.81, and the SST patterns from this
spring are similar to many low-activity years /Fig. 12/. The
SST pattern in 2022 was also similar, but the eastern Pacific
experienced above-normal activity.

There is medium confidence that the current negative PDO
pattern will persist through the hurricane season. One reason
is that SST forecasts made several months ahead tend to have
limited skill. Another reason is that the current negative PDO
signal partly reflects the synoptic-scale wind and pressure
patterns during the past months, influenced by La Nina,
which is forecast to completely fade. ENSO changes typically
lead PDO changes by months to seasons, with studies showing
ENSO leading PDO by 6 to 24 months. In addition, JAS Nino
3.4 values and JAS PDO values are correlated at about 0.50,
and the predictions for Nino 3.4 are well above zero /i.e., El
Nino/ in many models. The official ENSO outlook probabilities
indicate the relatively high likelihood of El Nino during a
low-activity era /Fig. 13, right/.  During El Nino years in
high-activity eras, tropical cyclone activity in the eastern
Pacific has almost a zero percent chance of a below-normal
season based on data back to 1970. During El Nino years in
low-activity eras, historical data indicate a 20 percent
chance of a below-normal season.  The current outlook, to
account for uncertainty in the activity era classification,
includes a 10 percent chance for a below-normal season.


NOAA FORECASTERS 

Climate Prediction Center 
Matt Rosencrans, Physical Scientist; Matthew.Rosencrans@noaa.gov 
Dr. Hui Wang, Physical Scientist; Hui.Wang@noaa.gov 
Dr. Daniel Harnos, Meteorologist, Daniel.Harnos@noaa.gov

National Hurricane Center
Eric Blake, Senior Hurricane Specialist; Eric.S.Blake@noaa.gov
Dr. Chris Landsea, Meteorologist; Chris.Landsea@noaa.gov

Atlantic Oceanographic and Meteorological Laboratory
Stanley Goldenberg, Meteorologist; Stanley.Goldenberg@noaa.gov

BACKGROUND INFORMATION: EASTERN PACIFIC HURRICANE SEASON

The eastern Pacific hurricane region covers the eastern Pacific
Ocean east of 140Ādeg W north of the equator. This area is one
of the most prolific tropical storm formation regions in the
world. Eastern Pacific storms most often track westward over
open waters, sometimes moving into the central and even western
Pacific hurricane regions reaching Hawaii and beyond. However,
some storms occasionally head toward the northeast, bringing
rainfall to the arid southwestern United States during the late
summer months. Some storms can also impact western Mexico or
Central America, especially early and late in the season.

The official eastern Pacific hurricane season runs from 15
May through 30 November. The peak activity typically occurs
during July through September. During the period 1991-2020,
the eastern Pacific seasonal averages were 15.4 named storms
/maximum 1-minute sustained 10 m wind speeds between 39-73
mph/, with 8.3 of those becoming hurricanes /maximum 1-minute
sustained 10 m wind speeds of at least 74 mph/ and 4.2 becoming
major hurricanes /maximum 1-minute sustained 10 m wind speeds
exceeding 111 mph, categories 3-5 on the Saffir-Simpson
hurricane scale/.

Eastern Pacific hurricane seasons exhibit long periods
of above-normal and below-normal activity in response to
large-scale climate patterns. Seasons also exhibit year-to-year
variability in response to ENSO. El Nino contributes to
decreased easterly vertical wind shear and favors above-normal
hurricane activity in this region. Historically, El Nino
is not associated with below-normal seasons. Conversely, La
Nina contributes to increased vertical shear and less overall
activity. Historically, 60 percent of La Nina episodes have
been associated with below-normal hurricane seasons, and only
28 percent have produced an above-normal season. However,
the ENSO impacts can be strongly influenced by the background
climate patterns. As a result, NOAA accounts for the combined
influences of both climate factors when making its seasonal
hurricane outlooks.

Measuring overall activity: The Accumulated Cyclone Energy
/ACE/ Index

The phrase "total seasonal activity" refers to the combined
intensity and duration of all eastern Pacific named storms and
hurricanes during a given season. The measure of total seasonal
activity used by NOAA is called the Accumulated Cyclone Energy
/ACE/ index /Fig 5/. The ACE index is a wind energy index,
defined as the sum of the squares of the maximum sustained
surface wind speed /knots/ measured every six hours for all
eastern Pacific named systems while they are at least tropical
storm strength.

NOAAs eastern Pacific hurricane season classifications

Reliable tropical storm and hurricane data for the eastern
Pacific began in 1971. The 1991-2020 mean value of the ACE
index is 108.7 x 104 kt2, and the median value is 97.2 x 104
kt2. The following season classifications are based on an
approximate 3-way partitioning of seasons based on the ACE
value, combined with the seasonal number of tropical storms,
hurricanes and major hurricanes.

Above-normal season: An ACE index above 115 x 104 kt2 /120
percent of the median/ and at least two of the following three
conditions: 17 or more named storms, 9 or more hurricanes,
and 5 or more major hurricanes.

Near-normal season: An ACE index in the range 80-115 x 104 kt2
/80 percent-120 percent of the median/, or an ACE value higher
than 115 x 104 kt2 but with less than two of the following
three conditions being met: 17 or more named storms, 9 or more
hurricanes, and 5 or more major hurricanes.

Below-normal season: An ACE index below 80 x 104 kt2 /80
percent of the median/.

Seasonal means and ranges during 1991-2020 of tropical
storms, hurricanes, and major hurricanes during above-normal,
near-normal, below-normal, and all, eastern Pacific hurricane
seasons.

Season Type
 Mean # of Tropical Storms
 Range of Tropical
Storms
 Mean # of Hurricanes 
 Range of Hurricanes
 Mean #
of Major Hurricanes 
 Range of Major Hurricanes 
 Below-
normal
 13.1
 7-18
 6.0
 3-11
 2.0
 0-4
 Near- normal
 15.1

10-18
 8.0
 6-10
 4.0
 2-6
 Above- normal
 18.6
 13-24
 11.6
9-16
 6.6
 4-9
 All Seasons
 15.4
 7-25
 8.3
 3-16
 4.2
 0-9
Seasonal means and ranges during 1991-2020 of tropical storms,
hurricanes, and major hurricanes forming in the eastern Pacific
during La Nina /7 cases/, ENSO-neutral /17 cases/, and El
Nino /6 cases/. The ENSO classification is provided by NOAAs
Climate Prediction Center, and is valid for the July-September
climatological peak of the eastern Pacific hurricane season.

ENSO Status
 Mean # of Tropical Storms
 Range of Tropical
Storms
 Mean # of Hurricanes 
 Range of Hurricanes
 Mean #
of Major Hurricanes
 Range of Major Hurricanes
La Nina
12.8

7-21
6.7
3-11
3.3
1-6
Neutral
17.1
9-25
9.1
5-14
4.2
0-9
El
Nino
15.0
12-18
8.5
6-13
5.5
3-9
 
$$