SHORT ANSWER
There are two separate worst windows, not one, and they sit on opposite sides of the calendar. Northern Hemisphere summer, roughly June through September, is the highest risk period for the US departure leg of your pet's trip, because airlines impose heat embargoes on live animal cargo when ground temperatures climb into the low to mid 80s Fahrenheit. Separately, Australian summer, December through February, is the highest risk period on the arrival end, since Melbourne, the only airport DAFF permits for live dog and cat arrivals, regularly sees heatwave days well above 35 degrees Celsius. The single worst overlap is early December, when Melbourne's heat is ramping up for summer at the same time Australia's Department of Agriculture, Fisheries and Forestry (DAFF) enters its annual holiday shutdown period with reduced regulatory capacity.
A heat embargo is not a judgment call made the day of your flight. It is a standing airline policy that activates automatically once forecast or actual ground temperatures at any point in the itinerary, origin, layover, or destination, cross a set threshold, generally in the low to mid 80s Fahrenheit (around 27 to 29 degrees Celsius). Pets spend real time on the tarmac and in cargo warehouses before and after loading, which is where the actual risk lives. Starwood Pet Travel has covered this in detail in our guide to summer heat embargoes and what they mean for your move, and the same mechanics apply whether the destination is Europe, Asia, or Australia.
Most general heat embargo guidance names Los Angeles as one of the more reliable US departure points during summer, and that holds up against the data. Los Angeles International Airport's average high even in August, its hottest month, sits around 75 to 83 degrees Fahrenheit, and coastal marine influence keeps temperatures well behaved for most of the season.
Dallas Fort Worth is a different story entirely, and this is worth stating plainly rather than folding it into general advice. DFW averages highs in the mid 90s Fahrenheit from June through August, with July and August regularly touching 96 to 98 degrees, according to the National Weather Service and independent climate data for the airport. Since Starwood's operational routing for Australia moves uses both Los Angeles and Dallas Fort Worth, a pet routed through DFW between June and September carries meaningfully higher heat embargo exposure than one routed through LAX during the same window. This is a real gap between general public guidance, which often treats "US summer" as a single risk category, and the specific airport your pet may actually be departing from. If your move is booked through DFW, treat May through September as a genuine planning constraint, not a background risk.
DAFF requires all dogs and cats to arrive directly into Melbourne International Airport, with no domestic transfers permitted from another Australian city. That means Melbourne's climate is not one of several options, it is the only one, and Melbourne's summer runs opposite the US calendar.
According to the Australian Bureau of Meteorology's climate statistics for Melbourne (Olympic Park), the mean maximum temperature in January sits at 26.8 degrees Celsius and February at 25.9 degrees Celsius. Those averages sound moderate, but they hide the real risk, which is heatwave spikes. Melbourne's all time recorded high is 46.4 degrees Celsius, and BOM's own January 2026 climate summary for the city recorded a peak day of 42.9 degrees Celsius that month alone. A single unexpected heatwave day at Melbourne during the December through February stretch can trigger the exact same kind of cargo embargo on the arrival end that a Dallas summer day triggers on departure, and because Melbourne is mandatory, there is no alternate airport to route around it.
Here is where the two risks compound instead of just alternating with the seasons. Australian summer heat begins ramping up through late November and into December, right as DAFF's Department of Agriculture, Fisheries and Forestry enters its annual holiday shutdown period. DAFF's own industry advice notice for the 2025 to 2026 holiday period confirmed reduced regulatory capacity and limited services from December 24 through January 2, with import and export inspection appointments during that window needing to be requested well in advance. That specific notice covers general trade services rather than pet imports directly, but it reflects the department wide pattern, and DAFF's own post entry quarantine facility at Mickleham is separately confirmed as closed on weekends and Australian public holidays year round, with reservation and inquiry services available only Monday through Friday, 8am to 4pm. A pet scheduled to land right around the holiday period is stacking rising Melbourne heat risk on top of a department running with less staff availability for documentation questions or booking changes.
As Adam Melton, VP of Strategic Initiatives at Starwood Pet Travel, explains: "People plan around the US side of the calendar because that's the part they can feel. Nobody in Dallas is thinking about a Melbourne heatwave in February when they're booking a move in October. But your import permit only stays valid for 12 months from your RNATT sample, and the final pre-export exam has to happen within 5 days of departure. If that narrow window lands during an Australian heatwave or over the DAFF holiday shutdown, you don't get a do-over without real cost and delay."
Because a US to Australia move already takes 6 to 8 months from the rabies vaccination and RNATT titer test alone, there is real opportunity to work backward from a safer arrival date instead of a convenient departure date. Late autumn or early spring in Melbourne, roughly March through May or September through November, avoids both the worst of Melbourne's summer heat and the Northern Hemisphere summer embargo season, since it falls in the moderate months on both ends of the trip. If your departure airport is DFW rather than LAX, build in extra flexibility for June through September regardless of the Australian end, and confirm with your pet relocation team which airport your specific booking uses well before you lock in vaccination dates, since that decision affects your entire summer risk exposure. For the full walkthrough of what your dog needs medically before any of this scheduling matters, see our guide to vaccinations and treatments required before flying to Australia.
Heat embargo timing comes up constantly in pet relocation communities, and Australia-bound moves are no exception. In a recent post on r/StarwoodPetTravel about summer heat embargoes, one commenter asked directly about a Malaysia to Australia move and whether the same seasonal risk applied outside the usual US to Europe conversation. The response underscored a point that holds everywhere: "Many airports and airlines impose heat embargoes so I would suggest checking with the airline you are using in Malaysia and keeping an eye on temperatures leading up to your pet's travel date". The same advice applies just as much to the Melbourne arrival leg of a US move as it does to the departure leg.