This week features a rather active pattern, with several chances for precipitation starting with today.
Tuesday – there is some small chance for scattered rain showers today associated with an area of low pressure that is currently located over North Carolina. However, this chance of rain will be primarily confined to areas south of the city. As the area of low pressure slowly moves offshore of the Mid-Atlantic states, the pressure gradient will strengthen, allowing for a persistent easterly wind to continue transporting cool, maritime air into the region. Temperatures will remain on the cool side, with highs similar to yesterday in the mid-70s.
Wednesday – conditions will improve somewhat as the aforementioned area of low pressure exits east over the Atlantic. We will still not be able to escape a cool, onshore wind from the northeast, so even though clouds will diminish, high temperatures will again struggle to reach 80.
Cold front approaches on Thursday
Thursday – the most substantial chance for rain this week will arrive with the passage of a cold front late in the day Thursday into the overnight hours. Warmer air from the southwest ahead of the cold front will translate to about average high temperatures in the low 80s under cloudy skies. As the cold front nears, showers and some thunderstorms will be possible. Current timing of the forecast models suggest that the bulk of the rain will not arrive until the evening hours.
Friday – conditions will improve Friday as high pressure builds in again in the wake of the cold front passing Thursday. Temperatures will drop back into the mid-70s with cooler, Canadian air filtering in from the north behind the front.
Tropical Storm Edouard?
Tropical wave off the coast of Western Africa
A vigorous tropical wave moved offshore of Western Africa earlier this week, and is being monitored for possibility of tropical storm formation later this week. Environmental conditions are forecast to remain favorable for development with low wind shear and warm sea surface temperatures. This storm may bring some impacts to the East Coast of the United States, but it is too early at this point to know the scope of that impact.
We had a solid round of rain from some showers and thunderstorms that passed through the area overnight. Over the weekend, high pressure will start to build into the area, ushering in a period of calm, pleasant, and seasonable weather.
Saturday & Sunday – clouds will diminish later Saturday, and by Sunday we’ll see mostly clear skies. Both days will feature high temperatures around 80.
Monday – as you see below, by Monday an area of high pressure will be firmly entrenched over our region. This high pressure area will persist through the middle of the week, giving us fair conditions and pleasant highs in the low 80s.
High pressure firmly entrenched in the Northeast for the beginning of next week.
Tuesday & Wednesday will look and feel essentially the same with highs in the low 80s and mostly sunny skies.
Our next chance of rain will be later in the week, perhaps Thursday into Friday with the arrival of a cold front from the west.
In the Tropics
There’s a tropical disturbance currently positioned offshore of Puerto Rico that will very likely become the 2014 Atlantic Hurricane Season’s third named storm, Cristobal. You can already begin to see the storm organizing, as over the last day or so, a circulation has become evident, and strong thunderstorms are forming in the northern semicircle are also apparent (see the classic cauliflower tops). Outflow bands are also forming up (thin wispy clouds north and northeast of the center).
High resolution satellite image of the tropical disturbance
This storm will fell some negative impacts from the high terrain of Hispaniola and Puerto Rico. As you can see, the southern semicircle is considerably less organized than the northern.
As for the track of the storm, you can see the rather large spread between the different forecast models, which is not surprising given that the storm is still in its early stages. Note that there is an outlier model solution showing landfall on the Mid-Atlantic. This is unlikely at this point, but worth noting. It seems, given the conditions ahead of the storm, that this will become Tropical Storm Cristobal in the next couple days, and may become Hurricane Cristobal shortly thereafter.
I haven’t been active on this blog the past couple of weeks as I’ve been in Costa Rica, however, the unfolding situation with Hurricane Iselle warrants a posting. I’ve observed Iselle as it formed from a tropical wave and then a tropical depression along the Inter-Tropical Convergence Zone off of the coast of Central America where I’m currently staying. Now, Iselle is closing in on the Hawaiian Islands and is set to make landfall on the Big Island this evening.
Despite the fact that the Hawaiian Islands lie near an active area for tropical cyclones, they are rarely impacted, in part due to the sheer vastness of open ocean versus the relatively small land area of the islands. During most years, a semi-permanent high pressure area that resides near the Islands also precludes the formation, strengthening, and penetration of cyclones into the region. This changes dramatically when El Nino conditions prevail, as they seem to be currently. Iselle will be the first landfalling hurricane to affect the Hawaiian Islands in 22 years since the devastating Hurricane Iniki of 1992. Fortunately, Iselle will be making landfall as a much weaker storm than Iniki, but regardless, it will still pack a serious punch.
Satellite image of Hurricane Iselle with Hurricane Julio following behind. To the far left, you can see Hurricane Genevieve.
Track Forecast
With less than 24 hours before landfall, the forecast track for Iselle is essentially zeroed in. The official track forecast cone has Iselle hitting the Big Island straight on. The center of the current forecast track envelope, should it hold up, has Iselle potentially making a direct hit on the eastern portion of the Big Island, with the eye of the storm skirting just south or perhaps directly over the Hilo area. I would hope for a northward deviation of this track, as this would spare the region from the strongest quadrant of the storm’s winds and waves (in the northern hemisphere, the strongest quadrant of a cyclonic storm is generally the northeastern quadrant). In the case of Iselle, due to its forecast west-northwest motion, the strongest quadrant should actually be the northwest, since the forward speed of the storm is added to the winds in that area.
After making landfall on the Big Island, Iselle is forecast to move to the south of the rest of the islands, passing closest to Maui. Because of uncertainty in the track forecast, it is entirely possible that Iselle could end up making multiple landfalls on different islands. However, I would anticipate these subsequent landfalls to be less serious in nature as Iselle should weaken substantially due to the influence of interaction with the mountainous terrain of the Big Island as well as increasing vertical wind shear from the north and west. There could still be some damaging storm surge and high winds in the other Hawaiian Islands, especially if the center of Iselle passes to the south of them.
Intensity Forecast
Iselle has been stubbornly persistent in maintaining minimal Category 1 status. Forecast models have been giving conflicting signals as to whether Iselle will be impacted by increased wind shear. Forecasters had not anticipated that Iselle would enter into a col between two high pressure centers, essentially an area of very low wind shear, think of it as a calm spot between two swirling eddies. Different forecast models are providing two divergent scenarios: (1) that Iselle continues to move in tandem with the col, allowing it to maintain current strength, or (2) Iselle leaves the col and experiences much higher wind shear.
No matter what, Iselle will be making landfall on the Big Island as either a minimal Category 1 hurricane or a very strong tropical storm. The real impacts of either scenario will be hardly discernible. Wind over the Big Island should pick up substantially this afternoon and evening first from the northeast, then north, and then switching to the south and southeast overnight. Sustained tropical storm force winds in the range of 50-65mph are expected depending on the specific locale. Wind gusts of up to 90mph are also possible in some locations. Offshore waves will build from 6 feet to as high as 31 feet closer to the center of the eye. I hope all people on the islands are making adequate preparations. Wind speeds as high as the ones forecast could easily shred even a decently well constructed roof. I’m not sure if the local government has issued evacuation orders, but if so, I hope all citizens of Hawaii will heed the call and take every necessary precaution to secure life and property. Let’s hope this Iselle weakens some more before it makes landfall.
Notes
In contrast to the Atlantic Hurricane Season thus far, this year’s Pacific Hurricane Season has been quite active, in part due to the influence of anomalously warm sea surface temperatures over the Eastern Pacific. These temperatures are indicative of what could be the start of an El Nino event. Hurricane Iniki also formed during a very strong El Nino event.
A quick update on TS Arthur, before a more substantial post later this afternoon. Based on the latest satellite imagery, it appears that Arthur is continuing to gather strength. You can see below that a central eye feature is beginning to form, and that spiral bands have now begun wrapping around the west side of the storm. While Arthur continues to struggle with dry air on its western side, it does seem that this is gradually being overcome. The inner core of the storm is displaying relatively symmetrical outflows, a sign that the storm is strengthening.
As of 11AM EDT, the National Hurricane Center analysis indicated that Arthur now has sustained winds of 60mph, and is moving north.
