Risk of Landfalling Hurricane in July, August Skyrocketing

**This post is dedicated to the 19 firefighters who perished in the Yarnell Hill Fire in Arizona.**

The threat of a tropical cyclone landfalling on the United States is quickly rising for July and August.

Forecasts from the CFS long range model are shown above in two charts- the Outgoing Longwave Radiation (OLR) and 850mb winds on top, and the OLR/850mb winds associated with the Madden-Julian Oscillation (MJO) on the bottom. Blues indicate areas of stronger tropical convection, while reds and oranges illustrate regions where storms are not as prevalent. Throughout July, it is being stressed that the MJO will want to hang around the waters immediately west and/or immediately east of southern India. The strength of this MJO pulse will vary, but it is likely we will see the enhanced tropical convection focus itself in the vicinity of India. When the enhanced convection is just west of India, as is shown on the second panel of the image above, the MJO is in Phase 1 of its eight phases. Each phase has different effects on the weather in the US, and each phase affects the chances of tropical cyclone formation differently. We'll dive deeper into the latter effect a bit later in this post.

Towards August, we see a change in the forecast. The rules for tropical convection and their associated colors are the same as the first image. In the bottom panel, rather than a small area of somewhat-dark blue colors, we now see a large swath of deep blues extending from India and into Oceania. When the enhanced tropical convection is centered due south of eastern China, this is referred to as Phase 2 or 3 of the eight-phased MJO. This is different from the Phase 1 chart we observed above, as the enhanced tropical convection has shifted further east. I have been worrying about August for intense tropical development in the Atlantic for a few days now, and this long range CFS forecast would seem to confirm my suspicions.

I talked earlier about how each phase of the MJO brings different areas of different potential for tropical cyclone formation. The chart above, from the NCEP, shows recorded tropical storm formation areas by each MJO phase (listed above each panel), as well as development in time periods when the MJO was too weak to be defined by a phase (bottom right panel). I mentioned how a Phase 1 (maybe Phase 2) MJO pattern was looking likely going into July (I know the chart says August, I will distinguish the two months in the following sentences). If we look at the chart above, on the top left panel, we see that development in Phase 1 in August was enhanced in the eastern Atlantic and Gulf of Mexico. The eastern Atlantic appears to have been lit up by tropical waves exiting the African coast, and the Gulf of Mexico tends to both accept a few of these tropical waves and also fire off its own low pressure systems that then develop further. In the July chart, eastern Atlantic is not as enhanced in Phase 1 as it is in August, so keep in mind any development in July would most likely be seen in the western Caribbean/Gulf of Mexico if we abide by a Phase 1 MJO for that month.
For August, I discussed my anticipation of a steady Phase 2 and 3 MJO pulse. Using the chart above to look at the Phase 2 panel (left center) and Phase 3 panel (bottom left), we see that the East Coast tries to attract some tropical attention, especially in Phase 2. The eastern Caribbean also lights up in Phases 2 and 3, but it is the Gulf of Mexico and Western Caribbean that retains its mark as the 'hotspot' for Atlantic development. Towards Phase 3 we see the African tropical wave system start back up, but I'm a little skeptical of its absence in Phase 2. Regardless, it's apparent that Phases 2 and 3 would allow some good chances at tropical development in the Atlantic.

In the long term, the GFS Ensembles are showing a lowering of sea level pressure anomalies off the western coast of Africa and along the 20N latitude line, as well as the raising of anomalies from western Europe into the waters offshore the Eastern Seaboard. This is in response to a large high pressure system across nearly all of the open Atlantic basin. When this kind of set-up appears, any tropical disturbances coming off the coast of Africa tend to be pushed south in a movement that favors entry into the Caribbean, potentially resulting in development in those waters or towards the Gulf of Mexico. While we cannot identify any particular disturbances in the waters between the 20N and 10N latitude lines in the image above, it is apparent that an anomalously low sea level pressure anomaly would indicate that the western coast of Africa may try and set off a few tropical waves during the last couple weeks of July.

The GFS Ensembles also show the normalized spread of sea level pressure between ensemble members, with individual members' high and low pressure areas shown in red (low pressure) or blue (high pressure) below. The abnormally high spread among ensemble members, as well as the presence of low pressure marks in the vicinity of this high spread tells me the ensembles could be hinting at the presence of a tropical wave for the middle of July nearly centered along the 20N latitude line west of Africa. Will this development actually happen? Chances are, regardless of development, this time period will attract some attention.

Andrew

Heat Records Quickly Falling Across Western US

A total of 31 high temperature records have been broken today, as the multi-day heat wave continues to bake much of the Western US.

Cities like Las Vegas and Reno in Nevada saw their high temperature records fall today, with the former location seeing an unconfirmed run at their all-time high temperature record at 116.1 degrees. Sacramento and Houston were among other big cities receiving broken high temperature records on this final day of June, with nearly 200 record high temperature-related records being set in the past 48 hours.

The heat wave looks to continue for at least another couple of days before the intense hot weather retreats and the weather pattern as a whole moderates. Remember to drink water often, and stay out of the sun as much as possible. This heat wave has already injured dozens, and it is possible the hospitals will be seeing more heat-related illnesses in the next few days if hydration and a relatively-normal body temperature is maintained.

Andrew

Active Weather Pattern Quieting Down

The active weather pattern we have seen in the last several weeks, where multiple significant tornadoes and severe weather outbreaks combined with the first two tropical cyclones of the Atlantic hurricane season, appears to be coming to an end in the next several days.

Projected mid level atmospheric flow turns firmly zonal by the start of the second full week of July, as strong low pressure originating from northeast Canada combines with the tendency of the atmosphere to favor ridging in the Northeast to regulate the flow over North America. When this period of zonal flow starts, no extreme hot or cold weather episodes are expected, and severe weather outbreaks are not encouraged. The lack of a wavy jet stream will permit the formation of a quiet weather pattern over North America.

Longer range forecasts favor the development of high pressure over the Rockies that may attempt to transition over into the Plains or even Ohio Valley areas. Whether that potential verifies remains to be seen. 

Andrew

Negative PDO Looking More Likely This Winter

The Negative phase of the Pacific Decadal Oscillation (PDO) appears likely as we head into this winter.

Shown above is an average of multiple globally-produced forecast models, showing sea surface temperature anomalies for November-December-January of 2013-2014. The circled area shows the trademark presence of the negative PDO- we see a body of above normal sea surface temperatures in the northeast Pacific, surrounded by below normal sea surface temperatures in the waters immediately offshore the coasts of western Canada and southern Alaska. While this covers two of the three big winter months, the PDO is called the Pacific Decadal Oscillation for a reason. We have been in the negative phase of the PDO for a while, and even without looking at this model suite, there is a decent probability that we will be in a negative PDO this winter.

In the temperature department, the negative PDO results in above normal temperatures for much of the nation. The core of the heat tends to be centered in the Southern Plains, but the Eastern Seaboard, Northeast, Midwest and Plains get in on above normal temperatures when the negative PDO arrives. It is important to note that the Pacific Decadal Oscillation is not the sole driver of weather; many other variables go into the equation of a seasonal temperature and precipitation pattern.

For precipitation, the negative PDO brings about a decidedly below normal trend in the Gulf Coast region and into the Southeast. While the severe drought observed just a year or two ago in the southern Plains has been alleviated to some point, it would only take one more winter of below normal precipitation to bring back some effects of that drought. Again, I cannot emphasize enough the fact that the PDO does not decide the entire seasonal trend- many other large and smaller-scale variables go into a seasonal weather pattern.

Andrew

Significant Heatwave Coming for Western US

A significant heatwave is on the way for many in the Western United States in the next week to 10 days (and beyond??)

The atmospheric pattern over the Western US will become incredibly favorable for major heat in the next 5-10 days as the mid level atmospheric flow becomes very wavy (called meridional). A very large depression in the mid level heights over the Midwest, Great Lakes and western Ohio Valley will force a very large ridge of high pressure to build over the Rockies and entire Western US. With model forecasts indicating this large depression in the atmosphere to persist over the Central US, it is very possible we could be in for a prolonged significant heat wave over the Western US.

Temperature forecasts from the GFS model have large parts of California breaching the 100 degree mark, with the maximum value just below 120 degrees. It is expected that these hot temperatures will persist throughout the mountains in California, Arizona, Nevada, Idaho, Oregon and Washington state in a multi-day hot weather event. This all begins in the next several days, and could very well persist for several days.

Remember to stay hydrated and take multiple breaks if you will be outside during this heat event.

Andrew