Updated 2004 Atlantic Basin outlook.

[USAwx1]

Sorry about the delay folks, I know i promised several in the chatroom that this would be finished Yesterday. This includes an update on the numbers, landfall and strike probabilities. Anyway, here it is.

Comments/feedback welcome.

Enjoy.
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This forecast is intended to update and replace our previous 2004 Atlantic basin tropical outlook posted back on April 28. A link to that thread is provided below:

http://66.98.251.192/phpbb2/viewtopic.p ... ht=#490919

As you are aware, our seasonal forecast posted on April 28th called for Thirteen Named storms, Eight Hurricanes, and Four Intense Hurricanes (Category 3 Strength or greater) (13-8-4). When it comes to Landfall/strike probability, it was determined that the East coast of the United States, portions of the Western Gulf Coast and areas in the Caribbean were especially susceptible to a major Hurricane landfall at some point during the 2004 season.

Purpose of this seasonal forecast update:

This Update will offer a broader and more in-depth inspection of United States landfall probabilities and a revision to the expected number of Named Storms, Hurricanes, and Intense hurricanes which we anticipate will form during the remainder of the 2004 season in the Atlantic basin based on the use of both statistical and analog methods.

We will also take a limited look at the Condition of various global indices (predictors) which are important for determining the outcome of the Atlantic tropical season.

The final forecast product will deal with the following:

1. The expected Number of Named Storms, Hurricanes, and Intense Hurricanes.
2. The expected Number of Tropical Cyclones expected to form in each month between August and November.
3. Expected Total Number of Named Storms, Hurricanes and Intense hurricanes to make landfall along the U.S. coastline.
4. Strike probabilities by state.

ENSO Update:

Our forecast issued in April centered largely on the assumption that slightly cool ENSO neutral conditions would continue through the remainder of the summer and into early fall (or about 3/4 of the way through the Atlantic basin tropical Season). It was also noted that a significant amount of uncertainty existed as to what the status of the ENSO may be thereafter. Below is the Equatorial Pacific SSTA verification for January-June 2004.

2004 1 24.60 0.09 25.92 0.30 28.83 0.68 26.74 0.23
2004 2 25.81 -0.22 26.46 0.10 28.59 0.58 26.86 0.17
2004 3 25.94 -0.54 27.16 0.08 28.43 0.34 27.10 -0.05
2004 4 25.32 -0.16 27.37 -0.03 28.75 0.34 27.84 0.17
2004 5 23.05 -1.28 26.72 -0.34 29.16 0.51 28.06 0.29
2004 6 21.60 -1.43 26.27 -0.11 29.17 0.54 27.76 0.27

Since April, we have noticed a sharp upturn in SSTA over the central and Western Equatorial pacific from about 120W longitude to the international dateline (along with persistent low-level westerly flow and enhanced convection (denoted by negative OLR anomalies over the region); meanwhile the eastern Equatorial pacific (From 120W longitude to the Coast of south America—or the NINO 1+2, 3.0 regions) has remained cooler than average as evidenced by the steeper slope of the equatorial thermocline and likely the result of persistent low-level easterly flow (at about 850H). The cooler than average Eastern Equatorial pacific and warmer than Average (Almost El Nino-like) central and Western pacific has contributed to the formation of a rather sharp and pronounced “Split” SSTA configuration over the Equatorial Pacific from west to east.

Those conditions have continued to intensify over the past few weeks as shown by the Weekly-averaged Equatorial pacific SST/SSTA verifications below:

02JUN2004 22.1-1.5 26.7 .0 28.1 .4 29.2 .6
09JUN2004 21.7-1.5 26.6 .1 28.0 .5 29.2 .6
16JUN2004 21.5-1.4 26.4 .0 27.8 .3 29.2 .6
23JUN2004 21.3-1.4 26.0 -.2 27.5 .1 29.1 .4
30JUN2004 21.0-1.4 25.6 -.4 27.3 .0 29.1 .5
07JUL2004 20.8-1.3 25.4 -.4 27.6 .4 29.4 .8
14JUL2004 20.9-1.0 25.5 -.1 27.7 .6 29.4 .8
21JUL2004 20.7 -.9 25.2 -.2 27.7 .7 29.4 .9

In the majority of years with similar conditions in the Equatorial pacific during the may-July period, have seen a slow transition from Neutral to El Nino conditions during the following months.

Below are some graphical representations:

http://www.osdpd.noaa.gov/PSB/EPS/SST/d ... 9.2004.gif
http://www.osdpd.noaa.gov/PSB/EPS/SST/d ... 1.2004.gif

Here are a few links to Weekly and Monthly SSTA verifications (Weekly Since 1990, and since 1950 monthly):

ftp://ftpprd.ncep.noaa.gov/pub/cpc/wd52 ... /wksst.for
ftp://ftpprd.ncep.noaa.gov/pub/cpc/wd52 ... oi.indices

The trend toward Weak El Nino conditions in the coming months is also supported by the majority of statistical and dynamical models from July.

http://iri.columbia.edu/climate/ENSO/cu ... _table.gif

A table of the data incorporated in the figure above can be accessed via the link below:

http://iri.columbia.edu/climate/ENSO/cu ... tml#figure

With this said we anticipate a slow evolution toward Weak El Nino conditions over the next few months. In the meantime however a continuation of the pronounced SSTA split in the Equatorial pacific is anticipated, with a persistence of Statistical ENSO neutral Conditions through October 2004. Weak El Nino conditions will likely develop thereafter; however this will come too late to significantly influence the remainder of the 2004 Atlantic tropical season.

The onset of El Nino conditions may also be delayed by the current long-term PDO negative phase, and westerly QBO.

ATC Overview:

As many of you are aware, much attention over the past several years has been focused on the reversal of the ATC (Atlantic Thermohaline Circulation) from the weak cycle (of 1970-1995), back to the strong cycle in 1995—which has persisted over the past 8 years (1995-2003). The ATC describes the strength of the temperature gradient and the distribution of heat and energy between the tropics and the poles, changes in oceanic salinity, Variations in Sea Surface Temperature relative to climatological normal and decadal changes in Atlantic Basin tropical Cyclone activity.

The current ATC strong phase implies a stronger than average temperature gradient between the tropics and the poles in response to more heat and energy being adevcted out of the tropics toward the North Atlantic. Sea Surface temperatures are warmer than average over the Far North Atlantic and Equatorial Atlantic. The AO (Arctic oscillation) and NAO (North Atlantic Oscillation) are frequently negative. Atlantic Tropical cyclone activity is above to much above average (especially with regard to the number of Hurricanes and Intense Hurricanes which form each season), and the PDO within the long term negative phase. Global temperatures are somewhat cooler than average as well.

Frequent and persistent high latitude blocking (as analyzed at the 500H level) was observed this past winter, and is associated with a mostly negative AO and NAO in the means—two patterns which are observed quite a bit during the ATC strong cycle and are a result of the SSTA configuration over the Atlantic basin.

http://www.cpc.noaa.gov/products/precip ... x.2003.gif
http://www.cpc.noaa.gov/products/precip ... o.2003.gif

Warm water has persisted over the Far North Atlantic (Surrounding Greenland, and Iceland), and across the Subtropical Atlantic. This SSTA configuration (commonly a precursor to a persistently Negative NAO and AO during the northern hemispheric winter) is also common during the ATC strong cycle.

Therefore, one can reasonably assume based on the NAO and AO verification from the previous winter, and the persistent SSTA configuration over the Atlantic basin that the ATC remains within the Tropical Cyclone-enhancing strong cycle.
Additionally, the warm SSTs over the Atlantic basin provide more available latent heat for tropical cyclone intensification.

QBO summary:

The stratospheric QBO (Quasi-Biennial Oscillation) represents the zonal wind at 30-50mb. The seasonal mode of the QBO has a profound impact on the intensity of tropical cyclones within 20N latitude of the equator. The September QBO state may also regulate the number of Intense Hurricanes (winds greater than 50
ms -1) (Gray 1988).

Tropical cyclone activity is normally enhanced in the Atlantic basin during periods when the stratospheric QBO is in the westerly phase, and suppressed in the easterly QBO phase. Research has suggested that twice the number of Intense Hurricanes occur in the Atlantic during the month of September when the QBO is westerly than those which occur in the Easterly phase in the Atlantic (Gray 1988). This theory is also supported by several of our analogs.

Because the QBO phase can be extrapolated several months into the future, we can confidently assume that the QBO phase will remain in the tropical cyclone enhancing westerly phase during the remainder of the 2004 Atlantic Basin tropical season.

Analog Method:

Various years with similar Oceanic and Atmosphere conditions as those described above (ENSO neutral conditions with a distinct split in the SSTA over the Equatorial Pacific, Warm SSTA over the far North Atlantic and Sub-tropical Atlantic indicative of a strong ATC, and west QBO), and Tropical cyclone numbers to date were used to compile our suite of Analogs for the remainder of the 2004 tropical season.

2004 AUG-NOV seasonal forecast:

Below are the number of named storms (NH), hurricanes (H) and Intense Hurricanes (IH) which are anticipated during the remainder of the 2004 Season:

Named Storms (NS): 12
Hurricanes (H): 8
Intense Hurricanes: 4

The only adjustments from the previous April outlook are to lower the number of named storms by one. Otherwise, in our interpretation, no changes were required.

Monthly forecast

Based on the preponderance of analogs, and other required adjustments as a result of various global patterns, the following are the TOTAL number of tropical cyclones which we expect to form in each individual month from AUG-NOV, and the percent of total which are expected for the entire season:

Total Number of Tropical Cyclones expected to for in AUG: 4 (33%)
Total Number of Tropical Cyclones expected to for in SEP: 5 (41%)
Total Number of Tropical Cyclones expected to for in OCT: 2 (16%)
Total Number of Tropical Cyclones expected to for in NOV: 1 (8%)

In the previous outlook a monthly forecast was not issued. We expect the highest number of storms on a monthly scale to occur in September—or about 41% of the total of 12 named storms forecasted to develop for the season as a whole. The percentages beside each value are to give persons an idea of how that particular month’s activity will relate to the total number of storms forecasted for the season, and which month is expected to have the highest activity relative to all others.

Note: No December storms are forecasted this year.

US Landfall Forecast:

Total Number of Tropical Cyclones expected to make landfall in 2004: 4 (30%)
Total Number of Hurricanes expected to make landfall in 2004: 2 (40%)
Total Number of Intense Hurricanes expected to make landfall in 2004: 1 (25%)

This data covers the Total Number of tropical cyclones expected to make landfall somewhere along the US coastline during the remainder of the 2004 Season. The percentages beside each value denote the relationship between the number of tropical cyclones, hurricanes and intense hurricanes which are expected to form in the Atlantic basin during the remainder of the season, and how many of those are forecasted to make landfall (in other words the total number making landfall in contrast to the total which are forecasted to develop).

Strike probabilities (by state):

The following (in order of 1 to 8) are the States MOST LIKELY to sustain a tropical cyclone landfall. The percentages beside each forecasted value denote the ratio of the total number of storms which Strike land (based on the analog mean) to those states which were impacted most frequently.

1. Texas (22%)
2. Florida (20%)
3. North Carolina (20%)
4. Louisiana (17%)
5. Maine (8%)
6. Mississippi (5%)
7. Maryland (2%)
8. New York (Long Island) (2%)

[USAwx1]

If anyone has a question, especially invloving strike probabilities in your state, please post it and i will respond.

NOTE: for those of you in the Carib. and islands, If you have questions regarding landfalls in your area, post them here also. I didn't issue a forecast for that area but would be more than happy to take questions and ALL will be responded to.

[Anonymous]

Nice work! Your discussion is appreciated.

[donsutherland1]

A superior job! Really fantastic reading.

I completely agree with the outlook.

Overall, things also appear well on track with Alex's development:

1950-2003 Select Data:

Tropical Depression of First Named Storm Formed July 1-July 31:
10/13 (77%) of seasons had 10 or more named storms; 2/13 (15%) had 8 or fewer named storms
…Average: 11.5 named storms; 7.3 hurricanes; 2.8 major hurricanes
…Most: 17 named storms; 12 hurricanes; 7 major hurricanes
…Least: 7 named storms; 4 hurricanes; 1 major hurricane

Named Storms by Month of Formation:
July: 46
August: 141
September: 190
October: 92
November: 23

Hurricanes by Month of Formation:
July: 25
August: 89
September: 126
October: 54
November: 16

Percentage of Named Storms Becoming Hurricanes by Month of Formation:
July: 54.3%
August: 63.1%
September: 66.3%
October: 58.6%
November: 69.6%

[cycloneye]

A complete outlook was this one USA covering every factor.

[Aquawind]

It's awesome reading..

[Rainband]

Excellent discussion

[Hurricanehink]

Wow, great outlook! We'll see how it verifies, but it looks good so far.

[USAwx1]

Thanks all for the kind words. BTW, Luis, I will PM you with the strike info for the Islands and PR later tomorrow.

A superior job! Really fantastic reading.

I completely agree with the outlook.

Overall, things also appear well on track with Alex's development:

1950-2003 Select Data:

Tropical Depression of First Named Storm Formed July 1-July 31:
10/13 (77%) of seasons had 10 or more named storms; 2/13 (15%) had 8 or fewer named storms
…Average: 11.5 named storms; 7.3 hurricanes; 2.8 major hurricanes
…Most: 17 named storms; 12 hurricanes; 7 major hurricanes
…Least: 7 named storms; 4 hurricanes; 1 major hurricane

Named Storms by Month of Formation:
July: 46
August: 141
September: 190
October: 92
November: 23

Hurricanes by Month of Formation:
July: 25
August: 89
September: 126
October: 54
November: 16

Percentage of Named Storms Becoming Hurricanes by Month of Formation:
July: 54.3%
August: 63.1%
September: 66.3%
October: 58.6%
November: 69.6%

Thanks for providing this Don. It would also seem to support the theory that this will A) be an active season in spite of the slow start and B) the idea that SEP will be the most active month (which is in touch w/ CLIMO anyway).

Once again thanks everyone.

[elw]

Wow! This was an excellent read, USA!