Heavy rain, high surf on deck with storms looming

Steven Gibbons/The OregonianSwells up to 20-feet will make for good surf watching along the Oregon Coast this week, like in this photograph from Heceta Head in January 2007.

Ready, set, soak.

A potent storm packing tropical moisture will aim a Pacific fire hose at the Northwest starting early tomorrow morning and lasting until Wednesday night, forecasters said today.

Although the system -- which is being carried along by a 200-mph jet stream -- will dump a half foot of snow in the Cascades, snow levels will soar to 7,000 to 8,000 feet by late tomorrow afternoon, changing that snow to rain.

The blast of Pacific rain could cause rivers and streams to quickly rise, especially on the Northern Oregon and Southwest Washington coasts, said Chris Collins, a forecaster for the National Weather Service in Portland.

National Weather ServiceTuesday's rainfall forecast.

National Weather ServiceWednesday's rainfall forecast

National Weather ServiceThursday's rainfall forecast

"I wouldn't be surprised to see five to eight inches of rain fall on the coastal mountains,'' Collins said. "Some places could see ten inches of rain."

Heavy rain could lead to minor tidal flooding on coastal rivers such as the Nehalem, Wilson and Trask thanks to the highest tides of the month and building seas, with swells of 16 to 18 feet on Wednesday and Thursday mornings. Tidal flooding could also occur on Willapa Bay in Southwest Washington as high tides near 11 feet.

Waves and strong ebb currents will also create 20 to 22 foot seas at the Columbia River bar, leading to very rough conditions. Strong rip currents are also likely along the coast, where winds will gust to 55 to 60 mph tomorrow and Wednesday.

At 1:40 p.m. this afternoon, the weather service issued a high wind watch for the North and Central Oregon coast through tomorrow evening. Gusts to near 60 mph could rake exposed headlands and beaches, with sustained winds of 40 mph.

Urban street flooding is also a distinct possibility, forecasters said, because of storm drains choked with leaves.

Portland has had measurable rain every day this month, with 2.09 inches through noon today, about half an inch above normal. Last year at this time, rainfall was a paltry 0.22 inches.

The next wave of rain could also set off landslides and debris flows.

"Here we go again,'' said George Taylor of Applied Climate Services in Corvallis. "It looks like a pretty wet one, but these fire hose storm are really hard to predict: If you're under the fire hose, you're going to get pretty wet...but they tend to spray erratically."

GOES WEST VISIBLEA conveyor belt of moisture is set to bring heavy rain, wind and possible flooding and landslides to the Pacific Northwest.

Officials will keep a close watch on areas burned during the Gnarl Ridge fire on the Northeast flanks of Mount Hood this summer, where bare hillsides have already lead to rapid runoff and small debris flows and landslides.

Debris flow could also occur on areas burned by the Kitson fire, which burned through steeply timbered hillsides four miles Southeast of Oakridge in September.

Rain stays in the forecast into Friday, but look for a drying trend by the weekend, with partly cloudy skies and temperatures in the high 50s.

2008 was not as hot

Meteorologists with the United Kingdom's weather service say the average global temperature this past year was about 57.7°F, the coolest this decade. Cooler water temperatures in the Pacific Ocean, referred to as La Nina, kept the atmosphere a little cooler last year, they say.

But this little drop is not necessarily a sign that global warming is slowing down. "Absolutely not," said Dr. Peter Stott, from the UKMET office. "If we are going to understand climate change we need to look at long-term trends."

Even though last year was a little cooler than recent years, 2008 would still rank as the tenth hottest year on record. The hottest was 1998. The UKMET climate office uses satellite data, ground weather stations and buoys to calculate the global temperature.

Top Ten in '08

Beginning Monday December 8th, The Weather Channel will be counting down the top ten weather events of 2008. I don't personally know what the top ten are. Apparently TWC doesn't trust me with that kind of top secret info. That's OK. I present to you now Mike Bettes' Biggest Weather Events of the Year!

1. Hurricane Ike
2. Spring/Summer Midwest Floods
3. Super Tuesday Tornado Outbreak
4. Record Midwest Snow Season
5. Hurricane Gustav
6. Mother's Day Outbreak
7. Prolonged Southeast Drought
8. California Wildfires
9. Rising Water Level at Lake Powell(+23')
10. Early March Midwest Snow Storms

I'm interested to see your top ten.

Another Earthquake

According to the USGS website, there was another small earthquake Wednesday at 1:21 PM. It was located 7 miles NNW of Guy or 47 miles north of Little Rock and it was a magnitude 2.5

This one is located well away from the cluster of small earthquakes which occurred near Magnet Cove last month. Did you feel it???

In the days to come, we'll be talking more and more about an active weather pattern for the state. The general theme will be below average temperatures for quite awhile.

Tropical Atlantic springing to life

[Updates follow original entry; latest as of 4pm EDT Thursday July 3.]

A surface low pressure center -- the most organized disturbance so far this season to emerge off the coast of Africa -- is in the eastern tropical Atlantic.

On the other side of the tropical Atlantic, a little doohickey (what appeared to be a sharp tropical wave at the surface but with a circulation spinning aloft) flared up Wednesday afternoon as it approached the Windward Islands.

What the location of the current two systems tells us is that we're shifting gears from June, when most tropical cyclone development takes place in the Gulf of Mexico and western Caribbean Sea, to July, which is a transition month on the way to August, when the balance tilts to the tropical Atlantic, and the basin as a whole becomes more conducive to development.

JUNE

EARLY JULY

MID JULY

LATE JULY

EARLY AUGUST

If that eastern Atlantic low were to become a tropical storm far to the east (it remains to be seen whether that will happen), such an occurrence would be unusually early. What would that portend for the remainder of the season? The peak is still 1-3 months away, and like with any long-range seasonal outlook, there's no way of knowing exactly what will happen far in advance ... and outcomes after early flare-ups can run the gamut.

For example, things got cranking early in the season in 2005, and we all now know how that season turned out. On this date (July 3) in '05, the depression that would go on to become already the third named storm (Cindy) formed; the center of Cindy would, in an eerie foreshadowing of what happened on August 29 of that year, pass just to the east of New Orleans.

However, as early as mid-June of the following year, as I similarly blogged at the time, the tropical Atlantic was lit up (below), and, Ernesto notwithstanding, the remainder of the 2006 season overall was like night and day compared to 2005.

The 2007 hurricane season was a rough one in some other countries, but with it and the '06 season having been much less destructive in the U.S. than the ones in 2004 and 2005, I hope there's not too much complacency. Not knowing what the outcome this year will be, let's hope for the best but be prepared for the worst. (Although a trite expression, it always rings true for hurricanes!)

THURSDAY MORNING UPDATE

With the surface circulation still well-defined, and convection (rain & thunderstorms) persisting around the center, the National Hurricane Center has designated the system in the far eastern Atlantic to be a tropical depression. After brushing Cape Verde with showers and gusty winds, it is not a threat to land for the foreseeable future. If T.D. #2 strengthens and becomes a tropical storm, it would get the name "Bertha."

Bertha was also the name of a hurricane in 1996 which formed in the Atlantic (not quite as far east) in early July, in fact its incipient circulation was first detected on satellite imagery on July 3! Bertha would go on to survive all the way across the Atlantic and make landfall on the North Carolina coast on the 12th of July.

UPDATE 11AM EDT THURSDAY JULY 3

The depression has been upgraded to Tropical Storm Bertha.

[Click on image for large version.]

UPDATE 4PM EDT THURSDAY

Per TWC's point of origin maps, and in double-checking the NOAA track climatology viewer, Bertha has apparently become an Atlantic tropical storm much farther east than any other storm on record so early in the season.

I've updated the map from earlier in this blog for the first 1/3 of July (no June storm is close) to put a red dot where Bertha was named (below). 1996's Bertha -- represented by the easternmost yellow dot -- had been the farthest east until eclipsed by 2008's Bertha.

Caveats:

-There may have been other tropical cyclones of storm intensity as far or farther east prior to the satellite era that were not officially designated to be tropical storms.

-Even during the modern era, when to designate a cyclone to be a tropical storm is a judgment made by the National Hurricane Center with some inherent subjectivity.

The latest TWC forecast track for Bertha can be found here.

Meanwhile, in the Gulf of Mexico ...

[Sunday update on the Gulf moisture and Tropical Storm Bertha follows original entry]

While all eyes are on Tropical Storm Bertha, it's in the middle of nowhere and of no immediate threat to land, and its ultimate destination is uncertain.

However, a tropical weather situation which could be life-threatening is imminent, and it just goes to show that you don't need a hurricane or even a named tropical storm for that to be the case.

There has been a big flare-up of convection (showers and thunderstorms) in the western Gulf of Mexico today, associated with deep tropical moisture, a weak surface trough of low pressure and low-level converging winds, and upper-level "divergence."

Tropical cyclone development is not expected at this time, but the potential exists for excessive rainfall in Mexico along with flooding and flash flooding (and mudslides in the eastern portion of the more mountainous inland terrain), as the wet pattern persists for the next few days.

[Crop of image from Wikimedia Atlas of the World under the GNU Free Documentation License]

Although the most extreme rainfall will occur south of the border (and let's hope this system does not achieve its worst-case scenario there), heavy showers are already affecting parts of southernmost Texas. That could eventually result in local flash flooding, but otherwise, any rain that falls in this region would be welcome and beneficial, given the extreme drought which exists.

[Radar image source: GRLevelX]

UPDATE 1PM EDT SUNDAY JULY 6

TEXAS

Continued good news in South Texas (well, except perhaps for folks' holiday weekend outdoor plans), as the combination of tropical moisture and other atmospheric triggers continues to bring rain, which is welcome as long as too much doesn't fall too quickly, and amounts are starting to add up. A statement just issued by the National Weather Service office in Brownsville indicates that in some places upwards of 4-5" has fallen so far since July 1, and additional locally heavy showers are around today.

MEXICO

Yesterday's big thunderstorm cluster in the satellite image above (early in the original entry) has given way to deep "convection" which is more sporadic over the western Gulf, but Mexico is not yet out of the woods. There's still a big area of deep tropical moisture, and the risk of flash flooding will still exist for the next couple of days, not only on and near the country's Gulf of Mexico coast but also on the Pacific side, where Tropical Depression Five-E is skirting that coast.

BERTHA

Bertha remains a weak tropical storm way out in the Atlantic. The National Hurricane Center said in their latest advisory, "it is much too early to determine if Bertha will eventually affect any land areas." Indeed, at least as far as any direct effects are concerned. (Indirectly, ocean waves which are generated can affect areas far away from storms.)

The place first in line near the potential path would be Bermuda, but that's not for a few days, and impacts there will depend on the exact track and intensity of Bertha. Although the Leeward Islands, Turks and Caicos, and southern Bahamas need to stay apprised of the storm's progress, they're not the most likely destination.

As for farther down the line, including the mainland United States ... A few folks who posted comments to my first entry on the storm have speculated where Bertha might go, and there have been some interesting forecasts out there on the web.

Inherent uncertainty exists in any 7-day track forecast, particularly so in this case, and there's also the question of how intense (or not) the tropical cyclone will get (it's not like Bertha is presently a Category 5 hurricane). The bottom line if you're in Myrtle Beach or the Outer Banks or anywhere else on the East Coast is that the storm is of no immediate threat, it has a long row to hoe and would have a lot of hurdles to get over to make landfall in the U.S. and do so as a hurricane, and even if that were to happen there's plenty of time to monitor the situation.

Stay tuned ...

100-year flood?

As illustrated by the above graphics, there was yet another round of heavy rain and flash flooding a few days ago in the central U.S., this time in southern Michigan and in the Kansas City metro area.

Fortunately, the deluges were localized and short-lived enough to not raise river levels significantly higher; although the weather pattern is such that there could be additional clusters of heavy thunderstorms at times in the Midwest, hopefully the worst of the large-scale flooding, which started really getting out of hand exactly a month ago (June 6-8), is mercifully over.

Just how epic was it? A 100-year flood? A 500-year flood? A gazillion-year flood? And how can, for example, "100-year" floods happen again and again within a much shorter time frame?

Here are the opening sentences from this recent Associated Press article on the Midwest flooding:

"Fifteen years ago, after the Midwest was swamped with what was pronounced a "100-year" or even a "500-year" flood, some folks figured they would never again see such a disaster in their lifetime. Some even dropped their flood insurance. Big mistake."

Why is such terminology so misunderstood? There are all kinds of problems and complications with it.

First of all, there's the overall total magnitude of a flood in a region (worst flood in X years) vs. the "recurrence interval" in a particular location, such as at one's home or business.

Misconceptions are furthered by the way things are portrayed in the media. "Unprecedented Midwest Flooding" blared one headline. "Flood of 2008 to be worse than Flood of '93" announced another. Which flood was actually worse? It depends. In some places the water was much higher in 2008; others such as the St. Louis metro area on the Mississippi River fared much better than 15 years ago, and overall the Great Flood of '93 was larger in scope than the 2008 flood. Locations such as Iowa City got hit hard both times.

Also, individual major weather events can occur very irregularly. For example, the area around Stuart and Port St. Lucie, Florida, had gone a long time since getting hit by the core of a strong hurricane making landfall from the Atlantic Ocean, yet within three weeks in 2004 the center of two such hurricanes (Frances and Jeanne) came in at nearly the exact same spot.

Then there's the length of those sorts of time periods (100 years, 500 years) vs. the length of the historical record for which good information is available. To confidently assess how frequently on average a very rare event occurs you'd need thousands of years of accurate data, which in this case doesn't exist. Absent that long period of record, values can be extrapolated from recurrence intervals of less-rare events, but that's a dicey proposition.

The amount by which the previous record crest of 20' in 1851 (and tied in 1929) was smashed in 2008 in Cedar Rapids would give the impression that 31+ feet must have an average recurrence interval of at least 150 years and probably much more. But we don't know when the last time that level was reached, nor do we know when it'll be reached again.

In Iowa City, given that the water level during the flood of 1993 substantially exceeded that of 1851, could a valid conclusion be drawn that it'd be at least 142 years before another flood of that magnitude? Look at the height of the crest on June 15, 2008 for the answer. But again, we don't know when that'll be equaled or topped! Will it be in 500 years or 100 years or 10 years or 1 year? (Let's hope not again in 2008!)

Add on top of all that: changes in climate, by whatever cause(s), can in turn change the frequency of weather extremes. (Maybe one reason why the extrapolations don't seem to be working very well lately?)

Plenty of material providing information about 100-year etc. floods has been readily available on the web, such as this and this from USGS, this from FEMA, and even this Wikipedia entry.

The upshot: a "100-year" flood means that based on available data (which might flawed), there's a 1-in-100 (1%) chance of a given location/elevation in a particular watershed being flooded in any given year -- not that a flood will necessarily occur exactly once every 100 years or on any other regular timetable.